TERM What is a satoshi? The smallest unit of bitcoin the ledger can record: 1 BTC = 100,000,000 satoshis. Named after bitcoin’s creator, it is the atomic denomination — all on-chain amounts are whole numbers of satoshis. SATOSHI (SAT) TERM What is a UTXO? An Unspent Transaction Output — a discrete coin on bitcoin’s ledger. Bitcoin has no account balances: a wallet’s "balance" is the sum of the UTXOs its keys can spend, like bills in a cash register. UTXO TERM What is block height? A block’s position in the chain, counted from the genesis block (height 0). The current height is bitcoin’s clock: halvings, difficulty changes and lock times are all scheduled by height, not by date. BLOCK HEIGHT TERM What is a confirmation? One confirmation means a transaction is included in a block; each later block adds another. Confirmations compound security exponentially — six (~1 hour) is the customary threshold for treating a payment as final. CONFIRMATION TERM What is a coinbase transaction? The first transaction in every block — the one that mints the block reward plus collected fees to the miner. It has no inputs: it is the only place new bitcoin is ever created. (The exchange borrowed the name.) COINBASE TRANSACTION TERM What is P2PK? Bitcoin’s original output format (2009): coins locked directly to a raw public key, predating addresses entirely. Most Satoshi-era rewards are P2PK — which is why explorers show famous early "addresses" as nearly empty. P2PK (PAY-TO-PUBKEY) TERM What does sat/vB mean? Satoshis per virtual byte — bitcoin’s fee unit. A transaction pays for the block space it occupies (its size in vbytes), not for the value it moves. The current sat/vB market decides how fast you confirm. SAT/VB TERM What is Replace-by-Fee (RBF)? A mechanism to replace an unconfirmed transaction with a higher-fee version of itself. RBF lets you start with a low bid and raise it only if the mempool demands — the civilized fix for a stuck transaction. REPLACE-BY-FEE (RBF) TERM What is Child-Pays-for-Parent (CPFP)? A fee-bumping technique where a new transaction (the child) spends an output of a stuck one (the parent) with a high fee, making the pair profitable to mine together. It is how the receiver can accelerate a payment. CHILD-PAYS-FOR-PARENT (CPFP) TERM What is a cold wallet? A wallet whose private keys never touch an internet-connected device — hardware devices, air-gapped machines, steel plates. Exchanges keep the bulk of customer coins in cold wallets; the biggest are the largest addresses in bitcoin. COLD WALLET