* Associated Press: A major international news agency.
* Advanced Placement (in education): College-level courses and exams offered in high school.
* Access Point (in networking): A device that allows devices to connect to a wireless network.
* Application Programming Interface (in software development): A set of rules and specifications that software programs can follow to communicate with each other.
* Action Potential (in biology/neuroscience): A brief electrical signal transmitted along a nerve fiber.
* Account Payable (in accounting): Money a company owes to its suppliers.
* Air Pressure (in meteorology): The pressure exerted by the weight of the atmosphere.
To know what "AP" means, you need to consider the sentence or situation where you saw it.