An Application Programming Interface (API) is a set of rules and protocols that allows different software applications to communicate and interact with each other. APIs enable developers to access and use the functionalities of other software systems, services, or platforms, without having to understand the underlying code.

APIs provide a standardized way for applications to exchange data and perform various operations. They can be used to retrieve information, send data, or execute specific tasks. APIs are commonly used in web development, mobile app development, and integration of different software systems.

APIs can be classified into different types, such as web APIs, library-based APIs, or operating system APIs. Web APIs, often based on HTTP protocols, allow applications to interact with web services and retrieve data from remote servers. Library-based APIs provide access to pre-built functions and modules, simplifying the development process. Operating system APIs enable applications to interact with the underlying operating system and utilize its functionalities.

APIs are typically documented with detailed specifications, including the available endpoints, request/response formats, authentication methods, and error handling procedures. Developers can use these specifications to integrate APIs into their applications effectively.