machine gun that is a portable automatic firearm

a machine gun that fires cartridges that would otherwise be used

a pistol-caliber, magazine-fed, individual automatic firearm

a type of machine gun which fires ammunition normally used in pistols

a weapon designed to fire a pistol cartridge in automatic mode and is employed in close quarters battle, where an assault rifle would be too bulky or may have too much penetration

An automatic firearm commonly firing pistol ammunition intended for close-range combat.

A submachine gun is a firearm that combines the automatic fire of a machine gun with the cartridge of a pistol, and is usually between the two in weight and size. They were first experimented with in the form of a stocked pistol being converted from semi to fully automatic, in the early 1900s.