What is an API?
An API (application programming interface) is a defined way for one piece of software to ask another for data or to do something.
When an app shows the weather, takes a payment or posts to a social network, it usually does it through another company's API. The API sets what you can ask for and what you get back.
Many web apps offer an API so developers can connect them to other tools, and AI apps often sell access to their models through one.

