Contrary to some people's belief, AR does NOT stand for Assault Rifle. The designation AR stands for the original designing company ArmaLite.
An AR is a firearm platform originally designed by ArmaLite and built by Colt,
an AR is a lightweight, intermediate cartridge magazine-fed, air-cooled rifle with a rotating lock bolt, actuated by direct impingement gas operation or long/short stroke piston operation.
It has been produced in many different versions, including numerous semi-automatic and selective fire variants.
It is manufactured with extensive use of aluminum alloys and synthetic materials.
Types of ARs include AR-15, AR-10 and AR-7.