What is a UTXO?

A transaction creates outputs, each with an amount and spending conditions. A UTXO is an output that has not been spent. An ordinary wallet adds up the outputs it controls to show a balance; pending payments and other restrictions can affect what is available to send.

A payment spends whole UTXOs and creates new outputs. If an input is larger than the payment and fee, the wallet usually creates another output for the change. The old output is spent once; the change is a new UTXO. This is where UTXOHub gets its name.

Unspent does not always mean spendable now. An output may have a time lock, require several signatures, or belong to someone who has lost the keys. Many outputs use addresses, but an address is not the output itself and can receive several separate UTXOs.