UTXO

Unspent Transaction Output — Bitcoin's data model for tracking ownership. Instead of account balances, every Bitcoin transaction consumes specific previous outputs (UTXOs) and creates new ones. Your wallet balance is the sum of UTXOs your address controls. UTXO enables natural parallelism (non-conflicting transactions can be validated independently) and intrinsic replay protection (spent outputs don't exist). Cardano uses an extended UTXO (EUTxO) model that attaches data and validator scripts to UTXOs for smart contracts.