A blank is a firearm cartridge that, when fired, does not shoot a projectile like a bullet or pellet, but generates a muzzle flash and an explosive sound (muzzle report) like a normal gunshot would. Firearms may need to be modified to allow a blank to cycle the action, and the shooter experiences less recoil with a blank than with a live round. Blanks are often used in prop guns for shooting simulations that have no need for ballistic results, but still demand light and sound effects, such as in historical reenactments, special effects for theatre, movie and television productions, combat training, for signaling (see starting pistol), and cowboy mounted shooting. Specialised blank cartridges are also used for their propellant force in fields as varied as construction, shooting sports, and fishing and general recreation.

While blanks are less dangerous than live ammunition, they are dangerous and can still cause fatal injuries. Beside the explosive gases, any objects in the cartridge (like wadding that may be keeping the propellant in place, or objects lodged in the barrel) will be propelled at high velocity and cause injury or death at close range.

Blank cartridges differ from the inert/fake ammunitions such as dummy cartridges and snap caps, which contain no primer or gunpowder to even produce flash and sound and are used for "cold" training or function-testing firearm actions. They are also different from the percussion caps used in cap guns, which also produce a sound of gunfire but only consist of the equivalent of the primer with no propellant, so they sound much softer.