Bitcoin: key words
Read the word, say the meaning out loud, then open the card.
Double-spending
Paying with the same digital money twice. Bitcoin was designed to stop it without a bank in the middle. Source
Hash
The result of scrambling any amount of data into a short, fixed-size output. Source
Proof of work
Finding a number that makes a block's hash start with enough zeros. It takes many guesses to find, and one check to confirm. Source
Mining
Spending computing power to process transactions, secure the network and add the next block, in return for a reward. Source
Block subsidy
The new bitcoin a miner may create in a block. It started at 50 BTC and has been 3.125 BTC since April 2024. Source
Halving
The cut in half of the block subsidy every 210,000 blocks, roughly every four years. Source
Satoshi (sat)
The smallest unit of bitcoin. 100,000,000 sats make 1 BTC. Source
UTXO
Unspent transaction output: an amount of bitcoin waiting to be spent. A wallet's balance is the total of its UTXOs. Source
Change output
The part of a transaction that sends the leftover back to the sender, because inputs can't be partly spent. Source
Fee rate
A transaction's fee divided by its size, usually in sats per virtual byte (sat/vB). Source
Mempool
A node's queue of transactions waiting to be added to a block. Source
Lightning Network
A network of two-party payment channels. Payments move off the main chain, and only opening and closing a channel go on it. Source