API stands for Application Programming Interface. An API is a connector/ intermediary between two software components. It is a set of definite protocols that makes the interface possible. The interface simply means the nature of requests and responses. How developers would form the request and responses comes under API documentation.
In simpler words, API allows two applications to communicate with each other. We use API when we check the weather on our phones or while sending and receiving messages on apps like Instagram or Facebook, etc.