What is Transaction?
A signed instruction consuming one or more UTXOs and creating new ones. Once confirmed it cannot be reversed.
A transaction lists inputs (references to UTXOs plus signatures proving the right to spend them) and outputs (new UTXOs with their spending conditions). Whatever value is left over after outputs becomes the fee.
Irreversibility is a design property, not a bug: it is what removes the need for a trusted intermediary. It is also why sending to a wrong address is unrecoverable, and why address verification matters.
Related terms
UTXO
An unspent transaction output: a discrete chunk of bitcoin locked to a condition. Bitcoin has no account…
How it worksConfirmation
A block containing your transaction. Each subsequent block adds another, making reversal exponentially more…
Transactions & feesFee rate (sat/vB)
What a transaction pays per virtual byte of the space it occupies. Miners prioritise by fee rate, not by…
Transactions & feesRBF (replace-by-fee)
A signalling mechanism that lets an unconfirmed transaction be replaced by a version paying a higher fee.
This definition is part of the Bitcoin Logical glossary. For the fuller explanation, start with Learn, or see the live numbers on The Bitcoin Signal.