Unspent transaction output
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In cryptocurrencies, an unspent transaction output (UTXO) is an output of a blockchain transaction that has not been spent, i.e. used as an input in a new transaction. Bitcoin is the most famous example of a cryptocurrency that uses the UTXO model.
In the case of a valid blockchain transaction, unspent outputs (and only unspent outputs) may be used to effect further transactions. The requirement that only unspent outputs may be used in further transactions is necessary to prevent double spending and fraud.
For this reason, inputs on a blockchain are deleted when a transaction occurs, whilst at the same time, outputs are created in the form of UTXOs. These unspent transaction outputs may be used (by the holders of private keys; for example, persons with cryptocurrency wallets) for the purpose of future transactions.
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- "Bitcoin UTXO Lifespan Prediction" (PDF). cs229.stanford.edu. December 11, 2015.