Alphabet phonétique international or International Phonetic Alphabet

Asian-Pacific Islander, an abbreviation often used in racial demographics

Armor-piercing incendiary, a type of armor-piercing shot and shell

API originally, Advanced Programming Interface, but now more commonly known by its near synonym, Application Programming Interface, is any defined inter-program interface. API or api may also refer to:

Air Pollution Index in Hong Kong

API gravity, a measure of the density of petroleum

American Petroleum Institute

Academic Programs International

Academic Performance Index

Active pharmaceutical ingredient

Australian Property Institute

Atmospheric pressure ionization

Api (mountain), a mountain in Nepal

Aviation Partners Inc.

Automated Processes Inc

Animal Protection Institute