a sidearm is a weapon, usually a handgun but sometimes a knife, dagger, sword, bayonet, or other mêlée weapon, which is worn on the body in a holster or sheath (in the case of a knife, dagger, sword, or bayonet) to permit immediate access and use. a sidearm is typically required equipment for military officers and is usually carried by law enforcement personnel. usually, uniformed personnel of these services wear their weapons openly, while plainclothes personnel have their sidearms concealed under their clothes. a sidearm may be carried alone, or as a back-up to a primary weapon such as a carbine, rifle, shotgun, or submachine gun.