nLocktime (one word, short for ‘transaction locktime’) works with nSequence fields to determine when a transaction is valid for inclusion in a block. If nLocktime is set to a block height or timestamp in the future, the transaction can’t be confirmed before that point. This is useful for escrow or delayed payout scenarios—though actual enforcement also depends on miner acceptance and the network’s median time. Many wallets default nLocktime to zero for immediate spending, while advanced scripts leverage it for time-based contract logic (together with CHECKLOCKTIMEVERIFY).