RBF (replace-by-fee)

A transaction flagged as replaceable can be rebroadcast with a higher fee as long as it is unconfirmed. Block producers then prefer the new version, which pays more.

It is the only way to speed up a Bitcoin send after the fact. Not every wallet exposes it, and the original transaction must have been sent with the right flag. In practice, sending with sensible fees in the first place is simpler than having to correct.