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 designed to allow instant and cheap Bitcoin transactions. While it is still experimental, it shows great promise for Bitcoin’s ability to scale.
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Block Height
Beginning at zero with the genesis block, all blocks are numbered in ascending order. This number is known as a block’s height. The current block height is simply the number of blocks in a given blockchain 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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