Glossary

Timelock

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A timelock allows a Bitcoin transaction to be created such that the recipient of the outputs cannot spend them for a specified time. The amount of time can be specified by either block height or Unix timestamp.

The timelock is specified in a dedicated part of each transaction. However, most transactions simply leave the timelock blank to avoid using this functionality. Timelocks are useful for creating Hashed Timelock Contracts (HTLCs), which drive the Lightning Network.

Related Terms
Lightning Network
The Lightning Network (LN) is a protocol enabling instant, cheap Bitcoin transactions. Still experimental, it shows great promise for scaling Bitcoin.
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Block height
Block height is a block's number in the chain, counting up from zero at the genesis block. The current height is the number of blocks in the chain minus one.
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Unix timestamp
A Unix timestamp is the number of seconds since January 1, 1970 UTC. Timestamps are used in blocks to ensure that blocks accumulate in a chronological order.
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Transaction
A transaction exists as a record of the transfer of bitcoin from one address to another. All transactions are recorded in blocks on the blockchain.
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