What is child pays for parent (CPFP)?
A way to make an unconfirmed parent and a child that spends it more attractive to miners as a package. Confirmation is not guaranteed.
The child pays enough fee to raise the fee rate of the parent and child together. Miners can evaluate the package, so both may be selected even if the parent's own fee rate is low.
A receiver may be able to create the child if their wallet supports spending the unconfirmed output. Senders can sometimes use CPFP too. Wallet support, the available output, fees and network policy all matter, and no package is guaranteed to confirm.
References
- Bitcoin Core, “Package Mempool Accept”.