Unspent Transaction Output (UTXO)
technical · blockchain
A discrete spendable output on a UTXO blockchain, similar to a digital coin that must be spent whole.
An unspent transaction output (UTXO) is a chunk of value created by a transaction and not yet consumed by a later transaction. Wallet balances on UTXO chains are the sum of spendable outputs controlled by the user's keys.
UTXO systems track coins rather than account balances. Every valid transaction consumes existing outputs as inputs and creates new outputs with locking conditions for future spending.
UTXO selection affects fees and privacy. Spending many small outputs increases transaction size, while combining unrelated outputs can reveal that the same wallet likely controls them.
Compare the broader design in UTXO versus account-based blockchains. Coin control explains how wallets let users choose which outputs to spend.
Related terms
Transaction
→A serialized state transition that a blockchain can validate, relay, and include in a block.
blockchain · technical
Block
→A batch of valid transactions added to a blockchain, linked to the previous block by a cryptographic hash.
mining · blockchain · security
Bitcoin (BTC)
→The first widely adopted cryptocurrency, using proof of work and an issuance schedule capped near 21 million BTC under current rules.
cryptocurrency · btc
P2PKH
→A common script type where the output can be spent by proving knowledge of the private key corresponding to a hashed public key.
script · address
P2SH
→A script type where the output is locked to the hash of a redeem script, enabling features like multi-sig.
script · address
Opcode
→An encoded instruction interpreted by a virtual machine or transaction script engine.
technical · scripting