The AR-15 is a lightweight, magazine-fed, air-cooled semi-automatic rifle with a rotating-lock bolt, actuated by direct impingement gas-operation or long/short stroke piston operation, and chambered for an intermediate caliber cartridge. The term "AR-15" stands for "Armalite rifle, design 15". The trademark "AR15" or "AR-15" is registered to Colt, which requires the term to be used only to refer to their products. Colt uses "AR-15" for its semi-automatic civilian rifles.