AC or Ac may refer to:
- Air conditioner, a machine that produces cool air
- Air conditioning, the mechanical process of cooling air in enclosed spaces
- Anarcho-capitalism, a form of free-market anarchism
- Ante Christum or A.C., a Latin term meaning "before Christ"
- Anthrocon, the largest furry convention in the world held in Pittsburgh, Pennsylvania
- Assessment center, a process to evaluate candidates for a job
- Average cost, in economics
- Acre, a unit of area with the symbol ac
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