A side arm or sidearm is a weapon, usually a handgun but sometimes a dagger, knife or other melee weapon, which is worn on the body in a holster to permit immediate access and use. A side arm is typically required equipment for military personnel and sometimes carried by law enforcement personnel. Usually, uniformed personnel of these services wear their weapons openly, while plainclothes personnel have their side arms concealed under their clothes. A side arm may be carried alone, or as a back-up to a primary weapon such as a rifle or carbine. Most standing army also have service pistols.