- (US) Any select-fire firearm that allows semi-automatic and fully automatic operation, and is used or was once used by a military organization.
- (US) A semi-automatic firearm that resembles a military weapon.
- (Semi-automatic firearm that resembles a military weapon): This term is considered pejorative by some. It is used primarily in a political context.
- There is no widespread official definition of assault weapon, and the meaning varies among different jurisdictions. However, according to defunct United States federal legislation, any semi-automatic rifle is an assault weapon if it has a detachable magazine and has two or more of the following: a pistol grip, a folding or telescoping stock, a bayonet mount, a flash suppressor, or a grenade launcher.