51% attack (s.v. "51 percent attack"): The ability of someone controlling a majority of network hash rate to revise transaction history and prevent new transactions from confirming. (†2305)
block (s.v. "Block"): One or more transactions prefaced by a block header and protected by proof of work. Blocks are the data stored on the block chain. (†2306)
block header (s.v. "Block Header"): An 80-byte header belonging to a single block which is hashed repeatedly to create proof of work. (†2308)
blockchain (s.v. "Block Chain"): A chain of blocks with each block referencing the block that preceded it. The most-difficult-to-recreate chain is the best block chain. (†2307)
double spending (s.v. "Double spend"): A transaction that uses the same input as an already broadcast transaction. The attempt of duplication, deceit, or conversion, will be adjudicated when only one of the transactions is recorded in the blockchain. (†2309)
fork (s.v. "Fork, Accidental Fork"): When two or more blocks have the same block height, forking the block chain. Typically occurs when two or more miners find blocks at nearly the same time. Can also happen as part of an attack. (†2310)
genesis block (s.v. "Genesis Block, Block 0"): The first block in the Bitcoin block chain. (†2311)
hard fork (s.v. "hard fork"): A permanent divergence in the block chain, commonly occurs when non-upgraded nodes can’t validate blocks created by upgraded nodes that follow newer consensus rules. (†2024)
hard fork : · Fork (a regular fork where all nodes follow the same consensus rules, so the fork is resolved once one chain has more proof of work than another)
· Soft fork (a temporary divergence in the block chain caused by non-upgraded nodes not following new consensus rules)
· Software fork (when one or more developers permanently develops a codebase separately from other developers)
· Git fork (when one or more developers temporarily develops a codebase separately from other developers (†2025)
M-of-N multisigs (s.v. "multisig"): A pubkey script that provides 'n' number of pubkeys and requires the corresponding signature script provide 'm' minimum number signatures corresponding to the provided pubkeys. (†2138)
Merkle Tree (s.v. "Merkle tree"): 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. (†2312)
mining (s.v. "Mining, Miner"): Mining is the act of creating valid Bitcoin blocks, which requires demonstrating proof of work, and miners are devices that mine or people who own those devices. (†2313)
proof of work (s.v. "Proof of Work"): A hash below a target value which can only be obtained, on average, by performing a certain amount of brute force work—therefore demonstrating proof of work. (†2314)
simplified payment verification (SPV) node (s.v. "SPV"): A method for verifying particular transactions were included in a block without downloading the entire block. The method is used by some lightweight Bitcoin clients. (†2202)
soft fork (s.v. "soft fork"): A softfork is a change to the bitcoin protocol wherein only previously valid blocks/transactions are made invalid. Since old nodes will recognize the new blocks as valid, a softfork is backward-compatible. (†2028)
unspent transaction output (UTXO) (s.v. "UTXO"): An Unspent Transaction Output (UTXO) that can be spent as an input in a new transaction. Not To Be Confused With · Output (any output, whether spent or not. Outputs are a superset of UTXOs) (†2212)
