What does 'API' stand for?

API stands for Application Programming Interface.

An API is a defined way for one piece of software to request data or actions from another. It specifies the available operations, the information a request must contain, and the form of the response. For example, a weather application can use a weather service’s API to request a forecast without knowing how that service stores or calculates its data.

APIs are not limited to the web. Operating systems expose APIs that let applications use files, windows, networking, and hardware. Libraries also provide APIs: a programmer can call documented functions without understanding every line of code inside the library. Web APIs commonly use HTTP methods such as GET, POST, PUT, and DELETE, often returning data in JSON format.

A frequent mix-up is expanding API as “Automated Program Interface” or “Advanced Programming Interface.” Those phrases are not the standard meaning. The word “interface” is important: an API is a boundary and set of rules that allows software components to communicate while keeping their internal implementation separate.