The lock of a firearm is the firing mechanism used to ignite the propellant. Types of lock include matchlock, wheellock, snaplock, snaphance, miquelet lock, doglock, flintlock, modern caplock/percussion cap, and experimental electronic types. Parts of the lock can include the serpentine (for matchlocks), wheel (for wheellocks), cock and frizzen (for flintlocks) or the hammer (for caplocks). A complete muzzleloader consists of lock, stock, and barrel.

Locks are typically spoken of when it comes to firearms which use loose ball and powder, and not to metallic cartridge breech-loading firearms, which are all percussion-based. In breech-loading weapons, the general mechanism for handling ammunition is known as the firearm action.

The term firelock was originally applied, as the name suggests, to the matchlock, but was later successively applied to the wheellock and then the flintlock as each was invented.^[1][2]