Side arm

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.

Uses
In a military setting, machine pistols are issued as personal defense side arms to paratroopers, artillery crews, helicopter crews or tank crews. Government security service bodyguards for VIPs and heads of state who need a weapon that can be concealed under clothing may have a fully automatic machine pistol as a side arm.

Historically in western armies, and in many contemporary armies, the issue of a side arm in the form of a service pistol is a clear sign of authority and is the mark of a commissioned officer or senior NCO. In the protocol of courtesy, the surrender of a commander's side arm is the final act in the general surrender of a unit. If no ill will is meant, and a strict interpretation of military courtesy is applied, a surrendering commander may be allowed to keep his side arm in order to exercise his right of command over his men. Similarly, many commanders on a local level have been anecdotally cited as having used the threat of their side arms to motivate troops, to varied effect.

Other eras
The term may also refer to swords and other mêlée weapons (e.g. the rapier, the tantō and wakizashi, the arming sword and the side-sword are all considered sidearms for their respective eras of use); the modern use of it usually pertains to pistols and similar firearms.