An assault rifle is a automatic rifle that uses an intermediate cartridge and a detachable magazine. Assault rifles are the standard infantry weapons in most modern armies. Assault rifles are categorized in between light machine guns which are intended more for sustained automatic fire in a light support role, and submachine guns, which fire a pistol cartridge rather than a rifle cartridge.
Examples of assault rifles include the Kalashnikov family, the M16 rifle, Enfield SA80, Heckler & Koch G36, FN F2000, and the Steyr AUG.

The term assault rifle is a translation of the german word Sturmgewehr (literally "storm rifle", as in "to storm a position"). The name was coined by Adolf Hitler to describe the Maschinenpistole 43, subsequently re-named Sturmgewehr 44, the firearm generally considered the first assault rifle that served to popularise the concept and form the basis for today's modern assault rifles.
The translation assault rifle gradually became the common term for similar firearms sharing the same technical definition as the StG 44. In a strict definition, a firearm must have at least the following characteristics to be considered an assault rifle:
It must be an individual weapon with provision to fire from the shoulder (i.e. a buttstock);
It must be capable of selective fire;
It must have an intermediate-power cartridge: more power than a pistol but less than a standard rifle or battle rifle;
Its ammunition must be supplied from a detachable magazine rather than a feed belt.
And it should at least have a firing range of 300 meters (984 feet)
Rifles that meet most of these criteria, but not all, are technically not assault rifles despite frequently being considered as such. For example, semi-automatic-only rifles like the AR-15 (which the M16 rifle is based on) that share designs with assault rifles are not assault rifles, as they are not capable of switching to automatic fire and thus are not selective fire capable. Belt-fed weapons or rifles with fixed magazines are likewise not assault rifles because they do not have detachable box magazines.
The term "assault rifle" is often more loosely used for commercial or political reasons to include other types of arms, particularly arms that fall under a strict definition of the battle rifle, or semi-automatic variant of military rifles such as AR-15s.
The US Army defines assault rifles as "short, compact, selective-fire weapons that fire a cartridge intermediate in power between submachinegun and rifle cartridges."