AC

Science:

Accurentum, a fictional chemical element from Star Trek
Acetaldehyde (also Ac), an organic ion
Acetate (also Ac), an organic ion
Actinium (Ac), a chemical element
Alternating current, a type of electric current
Anticipated Convection, the code for severe thunderstorm forecasts issued daily for the contiguous U.S. by the Storm Prediction Center
Armored Cable, a type of power cable used by electricians
atto coulomb (aC), an SI unit of electric charge
Axiom of choice, a mathematical set theory concept

Places:

Antigua and Barbuda, an obsolete NATO digram
Ascension Island, an island in the South Atlantic Ocean (ISO 3166-1 country code)
Atlantic City, New Jersey

Computing:

.ac, Internet top-level domain name for Ascension Island
.ac (second level), Internet second-level domain used to denote academic institutions in many countries
Anonymous Coward, in the Slashdot online environment
Authorization certificate or attribute certificate, a digital permission to use a service or resource

Transportation:

AC Schnitzer, an aftermarket tuner of BMW automobiles
AC Cars, a brand of automobile
AC Cobra, an Anglo-American sports car
Aero City, a bus built by the Hyundai Motor Company
Air Canada, as its IATA airline designator
Aircraft (usually A/C)
Algoma Central Railway, a now out-of-service railway in Northern Ontario, Canada

Ranks:

People:

Sport:

Music:

AC/DC, a rock group
Adult contemporary music, a music genre also used to describe broadcast radio stations

Entertainment:

The name of the ultimate computer at the end of time in Isaac Asimov's The Last Question
After Colony, an alternate timeline in the Gundam metaseries for the universe of Gundam Wing
"Alt Cataclius" or "After Cataclysm", a historical era in the timeline for the Dragonlance fictional universe
Animal Crossing, a real-time village video game for the Nintendo Game Cube and Nintendo DS
Armor Class, a combat-related parameter in the Dungeons & Dragons role playing game system
A robotic fighter that is under the player's control in the video game series Armored Core
Asheron's Call, a fantasy game in the massively multiplayer online role-playing (MMORPG) genre
Final Fantasy VII: Advent Children

Organizations:

Akademikernes Centralorganisation, the Danish Confederation of Professional Associations
Astronomy Club, common in schools and tertiary institutions

Miscellaneous:

Ac, another name for the Ansuz rune
Air conditioning (and air conditioner), the mechanical process of cooling air in enclosed spaces
Ante Christum, Latin for "before Christ"
Anthrocon, a furry fandom convention
Antichrist, in the Christian religion
Associación Civil, a title for non profit organizations in Spain
Atlantic College, one of the ten United World Colleges
Companion of the Order of Australia
Member of the National Assembly for Wales
Average cost in economics

See also