The name of the ultimate computer at the end of time in Isaac Asimov's The Last Question

Aleister Crowley, in "magickal" contexts

Aircraft (usually A/C)

Alice Cooper, hard rock, shock rock, and heavy metal singer

Antichrist, in the Christian religion

Atlantic City, New Jersey

Air conditioning (and air conditioner), the mechanical process of cooling air in enclosed spaces

AC/DC, a rock group

Air Canada, as its IATA airline designator

Armored Core, a video game series featuring the eponymous robotic fighter under the player's control.

Anal Cunt, a grindcore band.

Artificial consciousness

Aelod y Cynulliad, the title for Members of the National Assembly for Wales

Axiom of choice, a mathematical set theory concept

Adult contemporary music, a music genre also used to describe broadcast radio stations

Actinium (Ac), a chemical element

Alternating current, a type of electric current

A.C. Milan, one of the most storied clubs in that country

AC Cars, a brand of automobile

Abbreviation for Aquinas College located in Perth, Western Australia.

Athletic Club

AC Transit, a public bus transit system in Oakland, California

AC Cobra, an Anglo-American sports car

Animal Collective, an experimental musical collective.

Alpha Centauri, a star system in the constellation Centaurus

Abbreviation for Assumption College located in Worcester, Massachusetts USA.

Accurentum, a fictional chemical element from Star Trek

AC power, a net transfer of energy over a complete cycle of the alternating current waveform

"AC" is sometimes used as an abbreviation for "arcade". Therefore, it is often used as a suffix to designate a new or separate version of a game, or even merely as the abbreviation for a revision:

Assistant Commissioner of Police of the Metropolis

Anthrocon, a furry fandom convention

A.C. Green, former NBA player

Algoma Central Railway, a now out-of-service railway in Northern Ontario, Canada

Acetaldehyde (also Ac), an organic ion

After Colony, an alternate timeline in the Gundam metaseries for the universe of Gundam Wing

Austin Carr, former NBA player

Anterior commissure, a small bundle of nerve fibres that connect the right and left temporal lobes

.ac, Internet top-level domain name for Ascension Island

Anonymous Coward, in the Slashdot online environment

Average cost, in economics

Ayala Corporation, via its ticker symbol "AC".

AC Schnitzer, an aftermarket tuner of BMW automobiles

Authorization certificate or attribute certificate, a digital permission to use a service or resource

Acromioclavicular joint in humans and other animals, frequently injured in sport

Hyundai Aero City, a bus built by the Hyundai Motor Company

Civic Alliance Foundation, a Romanian NGO.

Another name for the Ansuz rune

Ad Council

Adenylate cyclase, an enzyme

Aircraftman (AC), or Aircraftwoman (ACW), is the lowest rank in the Royal Air Force and the air forces of several other Commonwealth countries, ranking below Leading Aircraftman and having a NATO rank code of OR-1. The rank was introduced on the...

Acetate (also Ac), an organic ion

Ante Christum, Latin for "before Christ"

Aezhumazhai vs Chitra, a forthcoming Tamil film.

Auto clickers, which are commonly referred to in MMORPGs as ACs.

Armor Class, a combat-related parameter in the Dungeons & Dragons role playing game system

Arctic Cooling, a Swiss manufacturer of heatsinks, cooling fans and computer cases.

Japan Ad Council

AC (complexity), a hierarchy of complexity classes found in circuit complexity

.ac (second level), Internet second-level domain used to denote academic institutions in many countries

Akademikernes Centralorganisation, the Danish Confederation of Professional Associations.

Associación Civil, a title for non profit organizations in Spain.

Anticipated convection, the code for severe thunderstorm forecasts issued daily for the contiguous U.S. by the Storm Prediction Center

attocoulomb (aC), an SI unit of electric charge

Aachen - a German city, using AC as number plate code

Acre - a Brazilian state, using AC as abbreviation. (See: ISO 3166-2:BR)

Alan Cox, Linux kernel developer

Associazione Calcio (Italian for "Football (soccer) Association"), an identifier frequently found in the names of football clubs in Italy, most notably:

Final Fantasy VII Advent Children, a movie sequel to the game Final Fantasy VII.

Arthur Curry, who goes by his initials during an appearance on Smallville (TV series)

Animal Crossing (series), a series of real-time village simulations by Nintendo.

Assassin's Creed, a platformer/stealth game for the Microsoft Windows, Xbox 360, and PlayStation 3 platforms.

Asheron's Call, a fantasy game in the massively multiplayer online role-playing (MMORPG) genre.

The Ace Combat series of combat flight simulator games.

Melty Blood: Act Cadenza, a two-dimensional fighting game featuring characters from Tsukihime.

Guilty Gear XX Accent Core, a two-dimensional fighting game, part of the Guilty Gear series.

Tekken 5 on the PlayStation 2 features a mode that allows one to play the arcade versions of Tekken, Tekken 2, and Tekken 3, labeled "AC".

Atlantic College, one of the ten United World Colleges.

post-nominal AC Order of Australia, Companion