American Revolution

Animal Rights, among animal rights activists

Argon, chemical symbol

Aortic Regurgitation, a heart valve disease

Androgen Receptor, a nuclear hormone receptor

Anti-reflective coating, a coating on lenses that allows better light transmission through the lens.

Accelerated Reader, educational reading assessment software

Aerolíneas Argentinas, IATA airline designator

Atlantic Records

The Arizona Republic, a newspaper published in Phoenix, Arizona

Artificial Respiration, a cardio-respratory technique for lifesaving.

the letter R

Accounts Receivable, an accounting term

Artist and repertoire

Armadillo Run, a physics-based, independently developed computer game.

Architectural Review, a publication of contempoary architecture.

Ar - Ancient Armenia the Ar was the god Sun.

Argent, the heraldic tincture of silver

Arabic language (ISO 639 alpha-2 language code)

.ar, the ccTLD for Argentina

Argentina, ISO 3166-1 alpha-2 and FIPS 10-4 digram country code

Appenzell Outer Rhodes, Swiss canton

Arkansas (United States postal abbreviations)

Autoregressive, stochastic process in Econometrics

Silver, in the field of numismatics (from the Latin Argentum)

Analytical Reagent, such as Zinc acetate, Mandelic acid or Perchloric acid

The AR-15, a popular Assault Rifle

Armalite, maker of the AR-15, a popular Assault Rifle

ar is a Unix archive format and handling tool

Augmented reality, an application of virtual reality in the real world

Action Replay, Video game device

Abandonia Reloaded, a freeware games web community.

Alternate Reality, a Primary Racial Trait in the 4X strategy computer game Stars!

Acoustic Research, a brand name of Audiovox

Aberdeen and Rockfish Railroad, (AAR reporting mark)

Armalite, an American arms manufacturer (e.g. AR-15 or any rifle of the same pattern)

Army Regulation, a publication in the family of field manuals, training manuals, etc.

Repair Ship, U.S. Navy hull classification symbol

the ᛅ rune of the Younger Futhark

Ar, largest city on the fictional planet Gor, from the the Gorean series by John Norman.

Arlesdale Railway, a fictional railway in the Railway Series by W.V. Awdry

Alex Rider, a fictional book series, by author, Anthony Horowitz; and the character with the same name.