EUTxO

Extended Unspent Transaction Output — Cardano's data model. Extends Bitcoin's UTXO model so each UTXO can carry arbitrary data (datum) and be governed by a validator script. Smart contracts on Cardano are validator scripts attached to UTXOs. Concurrency is structurally different: only one transaction per UTXO per block, so DeFi protocols split state across many parallel UTXOs to handle scale.