Technical Terms

Possibility of modifying the transaction ID of a transaction without affecting his validity.

A majority attack (usually labeled 51% attack or >50% attack) is an attack on the network. This attack has a chance to work even if the merchant waits for some confirmations, but requires extremely high relative hashrate.

Cryptocurrency alternative to Bitcoin

Anonymity is used to describe situations where the acting person's name is unknown

An application-specific integrated circuit (ASIC) /ˈeɪsɪk/, is an integrated circuit (IC) customized for a particular use, rather than intended for general-purpose use. For example, a chip designed to run in a digital voice recorder or a high-efficiency Bitcoin miner is an ASIC. Application-specific standard products (ASSPs) are intermediate between ASICs and industry standard integrated circuits like the 7400 or the 4000 series.

In computing, bandwidth is the bit-rate of available or consumed information capacity expressed typically in metric multiples of bits per second. Variously, bandwidth may be characterized as network bandwidth, data bandwidth, or digital bandwidth. This definition of bandwidth is in contrast to the field of signal processing, wireless communications, modem data transmission, digital communications, and electronics, in which bandwidth is used to refer to analog signal bandwidth measured in hertz, meaning the frequency range between lowest and highest attainable frequency while meeting a well-defined impairment level in signal power. However, the actual bit rate that can be achieved depends not only on the signal bandwidth, but also on the noise on the channel.

A Bitcoin Improvement Proposal (BIP) is a design document for introducing features or information to Bitcoin. This is the standard way of communicating ideas since Bitcoin has no formal structure.

Bitcoin is a digital currency invented by Satoshi Nakamoto. Nakamoto introduced the idea on 31 October 2008 to a cryptography mailing list, and released it as open-source software in 2009. The system is peer-to-peer and transactions take place between users directly, without an intermediary.These transactions are verified by network nodes and recorded in a public distributed ledger called the blockchain, which uses bitcoin as its unit of account.

A Bitcoin address, or simply address, is an identifier of 26-35 alphanumeric characters, beginning with the number 1 or 3, that represents a possible destination for a bitcoin payment. Addresses can be generated at no cost by any user of Bitcoin. For example, using Bitcoin Core, one can click "New Address" and be assigned an address. It is also possible to get a Bitcoin address using an account at an exchange or online wallet service.There are currently two address formats in common use:Common P2PKH which begin with the number 1, eg: 1BvBMSEYstWetqTFn5Au4m4GFg7xJaNVN2.

Bitcoin Core is the open source client of the Bitcoin Cryptocurrency. Initially, the software was published by Satoshi Nakamoto under the Name "Bitcoin" and later renamed to Bitcoin Core. The software validates the whole Blockchain including all transactions ever done. Moreover a wallet, which can be used to transfer funds, is included by default.

Newer P2SH type starting with the number 3, eg: 3J98t1WpEZ73CNmQviecrnyiWrnqRhWNLy.

A wallet which stores the information necessary to transact bitcoins. While wallets are often described as a place to holdor store bitcoins,due to the nature of the system, bitcoins are inseparable from the blockchain transaction ledger. A better way to describe a wallet is something that "stores the digital credentials for your bitcoin holdings" and allows you to access (and spend) them. Bitcoin uses public-key cryptography, in which two cryptographic keys, one public and one private, are generated. At its most basic, a wallet is a collection of these keys.

A block is a permanent record of data stored in the blockchain, acting like a page or ledger. Each block contains and confirms pending transactions. Roughly every 10 minutes, on average, a new block along with the transactions it contains is added to the blockchain through mining.

The number of blocks preceding a particular block on a block chain. For example, the genesis block has a height of zero because zero block preceded it.

Miners can mine blocks up to the 1MB fixed limit, but any block larger than 1MB is invalid.

Blocks are limited to 1MB in size.This limit cannot be modified without a hard fork.

The reward given to a miner which has successfully hashed a transaction block. Block rewards can be a mixture of coins and transaction fees, depending on the policy used by the cryptocurrency in question, and whether all of the coins have already been successfully mined. - See more at: http://www.blockchaintechnologies.com/blockchain-glossary#sthash.6WXoxn1B.dpuf

Bitcoin Core checks each block of transactions it receives to ensure that everything in that block is fully valid—allowing it to trust the block without trusting the miner who created it. This prevents miners from tricking Bitcoin Core users into accepting blocks that violate the 21 million bitcoin limit or which break other important rules.

A public ledger of all confirmed transactions in a form of a tree of all valid blocks (including orphans). Most of the time, "blockchain" means the main chain, a single most difficult chain of blocks. Blockchain is updated by mining blocks with new transactions. Unconfirmed transactions are not part of the blockchain. If some clients disagree on which chain is main or which blocks are valid, a fork happens.

-reindex throws away the block chain index and chain state (the database of all unspent transaction outputs), and rebuilds those from scratch. It is exactly like downloading the block chain again from peers, except the blocks already on disk are used.

In fault-tolerant computer systems, and in particular distributed computing systems, Byzantine fault tolerance is the characteristic of a system that tolerates the class of failures known as the Byzantine Generals' Problem. As reliable computer systems must handle malfunctioningcomponents that give conflicting information to different parts of the system. This situation can be expressed abstractly in terms of a group of generals of the Byzantine army camped with their troops around an enemy city. Communicatingonly by messenger, the generals must agree upon a common battle plan. However, one or more of them may be traitors who will try to confuse the others. The problem is to find an algorithm to ensure that the loyal generals will reach agreement. It is shown that, using only oral messages, this problem is solvable if and only if more than two-thirds of the generals are loyal; so a single traitor can confound two loyal generals. With unforgeable written messages, the problem is solvable for any number of generals and possible traitors.

The essential nature of the P2P network in Bitcoin was done explicitly to allow censorship resistance, such that even governmental agencies would be unable to stop the network and stop its payments.

This is usually considered in relation with mining centralization. It is considered the most dangerous form of centralization. It is probably the best known as well, although I would argue not always the most understood. The domination of mining by an increasingly small number of entities is a problem for a multitude of reasons, the most famous of which is the threat of the so-called ‘51% attack’.

A new opcode (OP_CHECKLOCKTIMEVERIFY) for the Bitcoin scripting system that allows a transaction output to be made unspendable until some point in the future.

A opcode that allows an output to conditionally specify how long it must be part of the blockchain before an input spending it may be added to the blockchain.

Every once in a while, an old block hash is hardcoded into Bitcoin software. Different implementations choose different checkpoint locations. Checkpoints prevent various DOS attacks from nodes flooding unusable chains and attacks involving isolating nodes and giving them fake chains.

OP_CHECKSIG is script opcode used to verify that the signature for a tx input is valid. OP_CHECKSIG expects two values to be on the stack. These are, in order of stack depth, the public key and the signature of the script.

It is is a proposed method of 'unsticking' transactions with small fees that have difficulty getting included into a block.

The coinbase is the content of the 'input' of a generation transaction. While regular transactions use the 'inputs' section to refer to their parent transaction outputs, a generation transaction has no parent, and creates new coins from nothing.

After a transaction is broadcast to the Bitcoin network, it may be included in a block that is published to the network. When that happens it is said that the transaction has been mined at a depth of 1 block. With each subsequent block that is found, the number of blocks deep is increased by one.

The consensus rules are the specific set of rules that all Bitcoin full nodes will unfailingly enforce when considering the validity of a block and its transactions. For example, the Bitcoin consensus rules require that blocks only create a certain number of bitcoins.

Developers regularly create intentional consensus forks by modifying Bitcoin client software. These changes upgrade or constrain the way that Bitcoin works — temporarily or permanently.

"a digital representation of value, not issued by a central bank, credit institution or e-money institution, which, in some circumstances, can be used as an alternative to money”,

It is a finite directed graph with no directed cycles. That is, it consists of finitely many vertices and edges, with each edge directed from one vertex to another, such that there is no way to start at any vertex v and follow a consistently-directed sequence of edges that eventually loops back to vagain.

DDOS attack is a type of DOS attack that occurs when multiple systems flood the bandwidth or resources of a targeted system, usually one or more web servers.[8] Such an attack is often the result of multiple compromised systems (for example a botnet) flooding the targeted system with traffic. A botnet is a network of zombie computers programmed to receive commands without the owners' knowledge.[13] When a server is overloaded with connections, new connections can no longer be accepted. The major advantages to an attacker of using a distributed denial-of-service attack are that multiple machines can generate more attack traffic than one machine, multiple attack machines are harder to turn off than one attack machine, and that the behavior of each attack machine can be stealthier, making it harder to track and shut down. These attacker advantages cause challenges for defense mechanisms. For example, merely purchasing more incoming bandwidth than the current volume of the attack might not help, because the attacker might be able to simply add more attack machines. This after all will end up completely crashing a website for periods of time.

Without a central authority or controlling party. Bitcoin is a decentralized network since no company, government, or individual is in control of it.

A distributed network is designed so that there is no central server or entity that others must connect to. Instead, network participants connect directly to each other. Bitcoin is a distributed network.

In computing, a denial-of-service (DoS) attack is an attempt to make a machine or network resource unavailable to its intended users, such as to temporarily or indefinitely interrupt or suspend services of a host connected to the Internet.

Double-spending is a failure mode of digital cash schemes, when it is possible to spend a single digital token twice. Since, unlike physical token money such as coins, electronic files can be duplicated, and hence the act of spending a digital coin does not remove its data from the ownership of the original holder,[1] some other means are needed to prevent double-spending.

BIP 107 – This BIP proposes a dynamic limit to the block size based on transaction volume

ECDSA is short for Elliptic Curve Digital Signature Algorithm. It’s a process that uses an elliptic curve and a finite field to “sign” data in such a way that third parties can verify the authenticity of the signature while the signer retains the exclusive ability to create the signature. With bitcoin, the data that is signed is the transaction that transfers ownership.

Ethereum is a decentralized platform that runs smart contracts: applications that run exactly as programmed without any possibility of downtime, censorship, fraud or third party interference.

The Finney attack is a fraudulent double-spend that requires the participation of a miner once a block has been mined. The risk of a Finney attack cannot be eliminated regardless of the precautions taken by the merchant, but the participation of a miner is required and a specific sequence of events must occur.

A flood attack is the process of sending thousands of transactions to "flood" the mempool, filling new blocks to the maximum size of 1MB, and subsequently delaying other transactions. It is easy to send transactions to yourself repeatedly, but it is made expensive with transaction fees.

Any computer that connects to the Bitcoin network is called a node. Nodes that fully enforce all of the rules of Bitcoin are called full nodes. Most nodes on the network are lightweight nodes instead of full nodes, but full nodes form the backbone of the network.

Any computer that connects to the Bitcoin network is called a node. Nodes that fully enforce all of the rules of Bitcoin are called full nodes. Most nodes on the network are lightweight nodes instead of full nodes, but full nodes form the backbone of the network.

Fungibility refers to the concept that every unit or subunit remains equivalent and identical to any other unit or subunit. It is the property of a good or commodity whose individual units are capable ofmutual substitution.

The gigabyte (/ˈɡɪɡəbaɪt/ gig-ə-byt or /ˈdʒɪɡəbaɪt/[1]) is a multiple of the unit byte for digital information. The prefix giga means 10^9 in the International System of Units (SI), therefore one gigabyte is 1000000000bytes. The unit symbol for the gigabyte is GB.

The Great Firewall of China, commonly known as "wall" is used by international, including Chinese, media to refer to legislation and projects initiated by the Chinese government (which is controlled by the Communist Party of China, CPC) that attempt to regulate the Internet in Mainland China.

A hardfork is a change to the bitcoin protocol that makes previously invalid blocks/transactions valid, and therefore requires all users to upgrade. Any alteration to bitcoin which changes the block structure (including block hash), difficulty rules, or increases the set of valid transactions is a hardfork

A hash algorithm turns an arbitrarily-large amount of data into a fixed-length hash. The same hash will always result from the same data, but modifying the data by even one bit will completely change the hash. Like all computer data, hashes are large numbers, and are usually written as hexadecimal. BitCoin uses the SHA-256 hash algorithm to generate verifiably "random" numbers in a way that requires a predictable amount of CPU effort. Generating a SHA-256 hash with a value less than the current target solves a block and wins you some coins.

A cryptographic hash function is a mathematical algorithm that maps data of arbitrary size to a bit string of a fixed size (a hash function) which is designed to also be one-way function, that is, a function which is infeasible to invert. The only way to recreate the input data from an ideal cryptographic hash function's output is to try a large number of possible inputs to see if they produce a match. Bruce Schneier has called one-way hash functions "the workhorses of modern cryptography". The input data is often called the message, and the output (the hash value or hash) is often called the message digest or simply the digest.

Invertible Bloom Lookup Tables (IBLTs) are a new (described in 2011) data structure that can be used to solve the set reconciliation problem. The idea of an IBLT is to squash together (using hashing and XOR) all of the transaction data into a fixed-size data structure. Then transmit that squashed data to a peer, who mostly knows what data you are sending them, but might be missing a few transactions or might be expecting that you put a few transaction in your block that you actually didn't.

The kilobyte is a multiple of the unit byte for digital information. The International System of Units (SI) defines the prefix kilo as 1000 (10^3); therefore one kilobyte is 1000 bytes. The unit symbol for the kilobyte is kB. In information technology kilobyte has traditionally also been used to denote 1024 (2^10) bytes, which arises from binary exponentiation common to digital circuitry. In this context, the symbols K and KB are often used when 1024 bytes are meant.

Lightning Network is a proposed implementation of Hash Time Locked Contracts (HTLCs) with bi-directional payment channels which allows payments to be securely routed across multiple peer-to-peer payment channels. This allows the formation of a network where any peer on the network can pay any other peer even if they don't directly have a channel open between each other.

Litecoin is a peer-to-peer Internet currency that enables instant, near-zero cost payments to anyone in the world. Litecoin is an open source, global payment network that is fully decentralized without any central authorities. Mathematics secures the network and empowers individuals to control their own finances. Litecoin features faster transaction confirmation times and improved storage efficiency than the leading math-based currency.

The locktime indicates the earliest time a transaction can be added to the block chain. Locktime allows signers to create time-locked transactions which will only become valid in the future, giving the signers a chance to change their minds.

The original and main network for Bitcoin transactions, where satoshis have real economic value.

This BIP (113) is a proposal to redefine the semantics used in determining a time-locked transaction's eligibility for inclusion in a block. The median of the last 11 blocks is used instead of the block's timestamp, ensuring that it increases monotonically with each block.

The megabyte is a multiple of the unit byte for digital information. The megabyte is commonly used to measure either 10002 bytes or 10242 bytes. The interpretation of using base 1024 originated as a compromise technical jargon for the byte multiples that needed to be expressed by the powers of 2 but lacked a convenient name.

The bitcoin Mempool (memory pool) is a collection of all transaction data in a block that have been verified by bitcoin nodes, but are not yet confirmed.

The act of using work done on one blockchain on more than one chain, using Auxiliary POW.

A branch connecting one or more leaves to the root

A Merkle hash tree is a tree of hashes in which the leaves are hashes of data blocks in, for instance, a file or set of files.

The root node of a merkle tree, a descendant of all the hashed pairs in the tree. Block headers must include a validmerkle root descended from all transactions in that block.

A tree constructed by hashing paired data (the leaves), then pairing and hashing the results until a single hash remains, the merkle root. In Bitcoin, the leaves are almost always transactions from a single block.

A micropayment is a financial transaction involving a very small sum of money and usually one that occurs online. A number of micropayment systems were proposed and developed in the mid-to-late 1990s, all of which were ultimately unsuccessful. A second generation of micropayment systems emerged in the 2010s.There are a number of different definitions of what constitutes a micropayment. PayPal defines a micropayment as a transaction of less than £5[4] while Visa defines it as a transaction under 20 Australian dollars.

Micropayment channels allow a customer to pay a merchant as little as a single satoshi, and do this time and time again over the course of hours or days. No matter how many payments the customer makes---and they can make millions---only two transactions appear on the Bitcoin blockchain and only two transaction fees are paid to miners.

Mining is a record-keeping service. Miners keep the blockchain consistent, complete, and unalterable by repeatedly verifying and collecting newly broadcast transactions into a new group of transactions called a block. Each block contains a cryptographic hash of the previous block, using the SHA-256 hashing algorithm, which "chains" it to the previous block thus giving the blockchain its name.

A person, a software or a hardware that performs mining.

In the context of cryptocurrency mining, a mining pool is the pooling of resources by miners, who share their processing power over a network, to split the reward equally, according to the amount of work they contributed to solving a block. A "share" is awarded to members of the mining pool who present a valid proof of work that their miner solved. Mining in pools began when the difficulty for mining increased to the point where it could take years for slower miners to generate a block. The solution to this problem was for miners to pool their resources so they could generate blocks more quickly and therefore receive a portion of the block reward on a consistent basis, rather than randomly once every few years.

When a Bitcoin miner finds a block, it receives newly minted bitcoins known as the "Block Reward". The reward (aka subsidy) is halved every four years and is responsible for bitcoin'scontrolled supply.

Nakamoto consensus is a name for Bitcoin’s decentralized, pseudonymous consensus protocol. It is considered as Bitcoin’s core innovation and its key to success. The consensus protocol doesn’t require any trusted parties or pre-assumed identities among the participants

Latency is a time delay between the cause and the effect of some physical change in the system being observed. Latency is physically a consequence of the limited velocity with which any physical interaction can propagate. This velocity is always lower than or equal to the speed of light. Therefore, every physical system that has spatial dimensions different from zero will experience some sort of latency, regardless of the nature of stimulation that it has been exposed to.

Part of a transaction which indicates the earliest time or earliest block when that transaction may be added to the block chain.

In cryptography, a nonce is an arbitrary number that may only be used once. It is similar in spirit to anonce word, hence the name. It is often a random or pseudo-random number issued in anauthentication protocol to ensure that old communications cannot be reused in replay attacks. They can also be useful as initialization vectors and in cryptographic hash function.

It is a hash of the transaction without the input scripts. SIGHASH_ALL says all inputs and outputs are included in the hash. These are the areas covered by the standard payment methods and they cannot be modified without invalidating the transaction.

A number intended to allow unconfirmed time-locked transactions to be updated before being finalized; not currently used except to disable locktime in a transaction

An off-chain transaction is the movement of value outside of the block chain.

An on-chain transaction - usually referred to as simply 'a transaction' - modifies the blockchain and depends on the blockchain to determine its validity an off-chain transaction relies on other methods to record and validate the transaction.

An orphan block rate that doesn't have a known parent in the longest block chain.

A block which is not a part of the valid blockchain, but which was instead part of a fork that was discarded.

A type of network where participants communicate directly with each other rather than through a centralized server. The Bitcoin network is peer to peer.

A 256-bit number used in ECDSA algorithm to create transaction signatures in order to prove ownership of certain amount of bitcoins. Can also be used in arbitrary elliptic curve arithmetic operations. Private keys are stored within wallet applications and are usually encrypted with a pass phrase.

Proof-of-stake (PoS) is a method by which a cryptocurrency blockchain network aims to achieve distributed consensus. While the proof-of-work (PoW) method asks users to repeatedly run hashing algorithms or other client puzzles to validate electronic transactions, proof-of-stake asks users to prove ownership of a certain amount of currency (their "stake" in the currency). Peercoin was the first cryptocurrency to launch using proof-of-Stake. Other prominent implementations are found in BitShares, ShadowCash, Nxt, BlackCoin, NuShares/NuBits and Qora. Ethereum has planned a hard fork transition from PoW to PoS consensus.

In order to be accepted by the rest of the network, a new block must contain a so-called proof-of-work.[50] The proof-of-work requires miners to find a number called a nonce, such that when the block content is hashed along with the nonce, the result is numerically smaller than the network's difficulty target. This proof is easy for any node in the network to verify, but extremely time-consuming to generate, as for a secure cryptographic hash, miners must try many different nonce values (usually the sequence of tested values is 0, 1, 2, 3, … before meeting the difficulty target.

Network propagation is the number of nodes (computers running a bitcoin client) that have heard about your transaction. Confirmations is how many blocks have included your transaction and how many blocks have linked onto that block.

A pseudorandom process is a process that appears to be random but is not. Pseudorandom sequences typically exhibit statistical randomness while being generated by an entirely deterministic causal process. Such a process is easier to produce than a genuinely random one, and has the benefit that it can be used again and again to produce exactly the same numbers - useful for testing and fixing software.

The public portion of a keypair which can be used to verify signatures made with the private portion of the keypair.

Allows a transaction to be time-locked, preventing its use in a new transaction until a relative time change is achieved.

The Bitcoin Relay Network is a system of peering between nodes in the network by creating a system of high-speed relay nodes for miners and merchants/exchanges. This system a) acts as a fallback in the case that the public Bitcoin network encounters issues and b) decreases block propagation times between miners.

The term "blockchain reorganization" is used to refer to the situation where a client discovers a new difficultywise-longest well-formed blockchain which excludes one or more blocks that the client previously thought were part of the difficultywise-longest well-formed blockchain. These excluded blocks become orphans.

Many nodes today will not replace any transaction in their mempool with another transaction that spends the same inputs, making it difficult for spenders to adjust their previously-sent transactions to deal with unexpected confirmation delays or to perform other useful replacements. The opt-in full Replace-by-Fee (opt-in full-RBF) signaling policy allows spenders to add a signal to a transaction indicating that they want to be able to replace that transaction in the future.

RIPEMD-160 is a cryptographic hash function based upon the Merkle–Damgård construction. It is used in the Bitcoin standard. It is a a strengthened version of the RIPEMD algorithm which produces a 128 bit hash digest while the RIPEMD-160 algorithm produces a 160-bit output. The compression function is made up of 80 stages made up of 5 blocks that run 16 times each. This pattern runs twice with the results being combined at the bottom using modulo 32 addition.

Scalability is the capability of a system, network, or process to handle a growing amount of work, or its potential to be enlarged in order to accommodate that growth. For example, it can refer to the capability of a system to increase its total output under an increased load when resources (typically hardware) are added.

To maintain consensus, all full nodes validate blocks using the same consensus rules. However, sometimes the consensus rules are changed to introduce new features or prevent network abuse. When the new rules are implemented, there will likely be a period of time when non-upgraded nodes follow the old rules and upgraded nodes follow the new rules, creating two possible ways consensus can break.

SCP (Stellar Consensus Protocol)is the a provably safe construction for FBA. Unlike most existing approaches to consensus, it enjoys four key properties: decentralized control, flexible trust, low latency, asymptotic security

Bitcoin uses a scripting system for transactions. Forth-like, Script is simple, stack-based, and processed from left to right. It is purposefully not Turing-complete, with no loops.

This BIP defines a new structure called a "witness" that is committed to blocks separately from the transaction merkle tree. This structure contains data required to check transaction validity but not required to determine transaction effects. In particular, scripts and signatures are moved into this new structure.

Selfish is an attack on the integrity of the Bitcoin network. This is where one miner,or mining pool, does not publish and distribute a valid solution to the rest of the network.

SHA-256 is a set of cryptographic hash functions designed by the National Security Agency(NSA). SHA stands for Secure Hash Algorithm. Cryptographic hash functions are mathematical operations run on digital data; by comparing the computed "hash" (the output from execution of the algorithm) to a known and expected hash value, a person can determine the data's integrity.

The selfish miner then continues to mine the next block and so on maintaining its lead. When the rest of the network is about to catch up with the selfish miner, he, or they, then release here portion of solved blocks into the network.

Smart contracts are computer protocols that facilitate, verify, or enforce the negotiation or performance of a contract, or that make a contractual clause unnecessary. Smart contracts usually also have a user interface and often emulate the logic of contractual clauses. Proponents of smart contracts claim that many kinds of contractual clauses may thus be made partially or fully self-executing, self-enforcing, or both. Smart contracts aim to provide security superior to traditional contract law and to reduce other transaction costs associated with contracting.

Smart property is property whose ownership is controlled via the Bitcoin block chain, using contracts. Examples could include physical property such as cars, phones or houses. Smart property also includes non-physical property like shares in a company or access rights to a remote computer.

A softfork is a change to the bitcoin protocol wherein only previously valid blocks/transactions are made invalid. Since old nodes will recognise the new blocks as valid, a softfork is backward-compatible. This kind of fork requires only a majority of the miners upgrading to enforce the new rules.

SPV mining is the term commonly used for 'less-than-full-node-validation' mining. It usually means that miners skip the verification of the block and the transactions within, and immediately start mining a new block referencing the just-solved block header. However, since they don't know what is in the last block, they have to mine without any transactions (except for the coinbase transaction), to be sure that they don't mine a block with transactions that conflict with transactions in the previous block.

A scheme to validate transactions without storing the whole blockchain (only block headers) and without trusting any external service. Every transaction must be present with all its parent and sibling hashes in a merkle tree up to the root. SPV client trusts the most difficult chain of block headers and can validate if the transaction indeed belongs to a certain block header.

Stratum is a proposal for an open source client-server "overlay" protocol that enables thin clients.

An attacker can attempt to fill the network with clients controlled by him, you would then be very likely to connect only to attacker nodes. Although Bitcoin never uses a count of nodes for anything completely isolating a node from the honest network can be helpful in the execution of other attacks.

The testnet is an alternative Bitcoin block chain, to be used for testing. Testnet coins are separate and distinct from actual bitcoins, and are never supposed to have any value. This allows application developers or bitcoin testers to experiment, without having to use real bitcoins or worrying about breaking the main bitcoin chain.

A timestamp is a sequence of characters or encoded information identifying when a certain event occurred, usually giving date and time of day, sometimes accurate to a small fraction of a second. The term derives from rubber stamps used in offices to stamp the current date, and sometimes time, in ink on paper documents, to record when the document was received. Common examples of this type of timestamp are a postmark on a letter or the "in" and "out" times on a time card.In modern times usage of the term has expanded to refer to digital date and time information attached to digital data. For example, computer files contain timestamps that tell when the file was last modified, and digital cameras add timestamps to the pictures they take, recording the date and time the picture was taken.

Network topology is the arrangement of the various elements (links, nodes, etc.) of a computer network. Essentially, it is the topological structure of a network and may be depicted physically or logically.

A small service charge added onto some transactions. The fee is paid to the miner that hashes the block containing the transaction.

Transaction fees are voluntary on the part of the person making the bitcoin transaction, as the person attempting to make a transaction can include any fee or none at all in the transaction

An identifier used to uniquely identify a particular transaction; specifically, the sha256d hash of the transaction.

A Treechain is a structure of more-tightly coupled sidechains. This structure, in theory, allows miners to mine at arbitrary variance without pooling, scaling of the system far beyond 7tps without asking permission, and other innovation at the edges, all with the same protections of the main Bitcoin network.

Soft forks are a feature of Bitcoin. Moreover, soft forks can be enforced by miners unilaterally, without others consent. That's because soft forks make rules more strict/add new rules, and these rules are enforced by miners.

An Unspent Transaction Output (UTXO) that can be spent as an input in a new transaction.

A UTXO commitment is a hash of all of the data in the UTXO set. It is validated by all of the proof of work that was built on top of it

The goal of the cost metric approach is to tie consensus rules to actual resource requirements. The idea is that cost of a block is a function of certain block properties. As an example, the block cost could be represented by a weighted sum of block size, validation cost and utxo growth.

A transaction in which the merchant is happy to provide a product or service before the bitcoin’s transmission has been confirmed by a miner and added to the blockchain. It can carry a risk of double spending.

A zero-knowledge proof is a method by which one party can prove to another that a given statement is true, without conveying any additional information apart from the fact that the statement is indeed true.