'AP' originates from English as an initialism formed from the capital letters of multiword terms. Newer common usages include 'Advanced Placement' (a 20th-century U.S. program) and technical abbreviations such as 'armor-piercing' (military terminology). An older and long-established usage is as the initialism for 'Associated Press' (the U.S. news agency).

'AP' developed by taking the initial letters of multiword English names and terms (e.g., 'Associated Press'); over time the same letter pair was reused for other phrases like 'armor-piercing' and later 'Advanced Placement', producing multiple distinct senses of the abbreviation.

Initially, the sequence 'A' and 'P' identified a specific organization ('Associated Press'), but over time it became a general initialism applied to different phrases and technical terms; its meaning now depends on context.