CheckSequenceVerify (CSV) was introduced in BIP-112 and works with relative locktimes specified in BIP-68. Unlike CLTV’s absolute reference, CSV ties the waiting period to the age of the UTXO. For example, you can require 100 blocks to pass after the transaction that created an output before that output can be spent.

This functionality is crucial for advanced payment channel designs, allowing participants to enforce penalty or closing conditions if one party tries to cheat. It’s another piece in Bitcoin’s evolving toolkit for flexible, trust-minimized contracts and layer-2 protocols.