Address

The secret number that authorises spending. Whoever has it controls the coins.

Derived from the private key; an xpub lets software see all your addresses but not spend.

SegWit was a 2017 upgrade that moved signatures into a separate part of the transaction. It fixed a long-standing bug, made room for more transactions and opened the door to the Lightning Network.

Taproot is a 2021 upgrade that added Schnorr signatures and a way to hide unused spending conditions. Complex wallets, such as multisig, can look like ordinary single-key payments.

Bitcoin has no account balances. Your wallet holds separate “coins” called UTXOs, like notes in a purse; a payment spends some of them and creates new ones, including change back to you.