A dummy cartridge or dummy round is a round that has no primer or propellant to send its projectile downrange, thus rendering the cartridge inert. These rounds are generally used for dry-fire practice or for demonstrations of how malfunctions occur. They can also be used in "ball and dummy" drills to simulate weapon malfunctions, and to improve trigger control.
Snap caps serve the same purpose as dummy rounds, but are not truly cartridges. They are manufactured to the same dimensions as the actual cartridge. The primer pocket is filled to give the firing pin a surface to hit, to prevent gouging of the bolt or slide during dry fire, and to prevent undue wear on the striker or firing pin.