A shotgun is a type of firearm that can be used to fire many different types of ammunition. The most common type of ammunition is called "shot", which consists of multiple small pellets which spread out when fired. However, since the energy of the blast is distributed amongst each piece of shot, the velocity of each piece is relatively low. This limits the effective range of a shotgun.
Because of their stopping power, high probability of causing wounds, and low chance of collateral damage, shotguns are favored by police forces and homeowners as a self-defense weapon. The United States legal code (18 USC 921) defines the shotgun as "a weapon designed or redesigned, made or remade, and intended to be fired from the shoulder, and designed or redesigned and made or remade to use the energy of the explosive in a fixed shotgun shell to fire through a smooth bore either a number of ball shot or a single projectile for each single pull of the trigger."