Bitcoin glossary
UTXO
Unspent Transaction Output — the actual form bitcoin takes on the blockchain.
A UTXO (Unspent Transaction Output) is how bitcoin actually exists on-chain: not as account balances, but as discrete outputs of past transactions that have not yet been spent. Your wallet balance is the sum of the UTXOs your keys can unlock; sending bitcoin consumes UTXOs and creates new ones, like paying with bills and receiving change.
The model matters practically: many small UTXOs cost more in fees to spend later, which is why experienced users consolidate them when fees are low.