Replace By Fee (RBF)
The sender in an unconfirmed transaction creates a new, higher fee transaction spending some of the same inputs as the transaction being replaced. Often the new transaction will be confirmed instead of the original transaction.
Child Pays for Parent (CPFP)
The recipient in an unconfirmed transaction spends their unconfirmed transaction output, increasing the effective fee of the original transaction. A miner can't confirm the new (child) transaction without also confirming the original (parent) transaction.
