API stands for Application Programming Interface. Sometimes it is also called Application Program Interface. An interface can be thought of as a contract because it defines a set of rules that must be followed in order for two entities to communicate or interact with each other. An API defines a set of rules and protocols for how one system can access and make use of the functionality and data provided by another system . A web API is a set of rules and protocols that define how two systems can communicate with each other over the internet. It allows one system (such as a server) to expose certain functionality or data to other systems (such as mobile application). Web APIs are typically accessed over HTTP or HTTPS, and they can use a variety of data formats (such as JSON or XML) to exchange information. They are often used to enable integrations between different systems, or to allow developers to build applications that interact with a web-based service or platform. The API docume