Timelock

Definition

A timelock is a condition that restricts when a transaction or spending path can become valid. Bitcoin supports absolute constraints tied to a block height or time threshold and relative constraints measured from an earlier output's confirmation. These mechanisms support arrangements such as payment channels, delayed recovery paths, and refunds when another party does not complete an exchange. A timelock usually defines the earliest permitted spending point rather than automatically sending funds at a scheduled moment. Someone still needs to construct, authorize, and broadcast an appropriate transaction, and confirmation depends on mining. Blockchain time measurements also should not be treated as precise wall-clock appointments. A locked output may contain alternative spending paths with different conditions, so the full script or policy matters. Understanding which party can spend, after which trigger, and through which authorization path is essential to interpreting the protection a timelock provides.