What is an API? A software go-between that permits communication between two or more computer platforms, applications, or systems is known as an application programming interface (API). APIs are all around us, even if you don't realize it. An API is used every time you use a taxi app, make a mobile payment, or modify the temperature of your home from your phone. Consider an API to be the intermediary between two applications. And, even though we can't see it, APIs put in a lot of effort.