Other
- Air Passenger Duty, an excise duty levied on passengers flying from UK airports
- Air Protection Division, A fictional Security Service
- Albany Port Railroad Corporation, a railroad company in New York
- Alianza por la Democracia
- Alpha Phi Delta (ΑΦΔ), a fraternity
- Antisocial personality disorder, in psychology
- Avoidant personality disorder, in psychology
- Appledore (Kent) railway station, from its National Rail code
- Avalanche photodiode, a device for counting photons
- Average Per Day
- High speed transport, a type of vessel, from its United States hull classification symbol "AP" for transport and "D" for destroyer.
- Automotive Performance Development
Read more about this topic: APD