CLTV, introduced by BIP-65, is like a timed lockbox for your BTC. You specify a future block height or timestamp in the script. Until the blockchain reaches that time, the funds cannot be spent.

This feature enables use cases such as time-locked escrows or delayed payouts. For instance, you might schedule a payment to become spendable next month, or enforce a holding period in a contract. CLTV opened the door to more sophisticated scripting and layer-2 applications, paired with OP_CSV for relative locktimes (BIP 68/112).