(countable) An AR-15 personal semi-automatic rifle, M-16 assault rifle, M-4 carbine, derivative or related gun; the Armalite AR family and derivatives.
In its August 2003 issue, while the ban was still in effect, Guns & Ammo ran a feature story titled “Stoner’s ‘Black Rifle’ Marches On,” subtitled “The basic AR platform has been refined, improved, upgraded, power-boosted and accurized.” 2017 December 14, David Heath, Elise Hansen and AJ Willingham, CNN Design: Joyce Tseng, “How an ‘ugly,’ unwanted weapon became the most popular rifle in America”, in CNN:
(countable, informal) An assault rifle or automatic rifle.
(abbreviation, alt-of, initialism, plural, plural-only, uncountable) Initialism of accounts receivable.
Near-synonyms: MR, mixed reality, spatial computing, CPS, cyber-physical system
(Cover started out as a company in the AR and VR business, but moved into the virtual talent sector; Ichikara is a startup designed to support their virtual talent) 2020 December 22, Tyler Colp, “The Vtuber Industry: Corporatization, Labor, and Kawaii”, in Vice, archived from the original on 22 Dec 2020:
(abbreviation, alt-of, countable, initialism, slang, uncountable) Initialism of alternate reality.
As I was going over the AR book for my status change, I read several other ARs I believed the institution was violating so I decided to ask about them at the meeting. 1984 August 18, Karen J. Cox, “Women In Cages”, in Gay Community News, volume 12, number 6, page 7:
(abbreviation, alt-of, countable, initialism, uncountable) Initialism of androgen receptor.