Dud
A cartridge that fails to fire when the primer is struck. Distinct from a hangfire, which fires after a delay, and a squib, which fires weakly.
A dud is a complete ignition failure. The firing pin hits the primer and nothing happens. Causes range from a dead or improperly seated primer to contaminated priming compound or a light firing-pin strike from a worn spring.
Treat any failure to fire as a possible hangfire first. Keep the muzzle pointed downrange and wait a good thirty seconds before opening the action, because a delayed ignition can still send the bullet. Only after that pause do you cycle the dud round out and inspect it.