An Application Programming Interface (API) is a set of protocols, routines, and tools for building software applications. APIs define how software components should interact and communicate with each other, providing a standardized way for developers to integrate different services and applications.

In simpler terms, an API acts as an intermediary between two applications or software components, allowing them to communicate and share data with each other. For example, if you use a weather app on your phone, the app is likely using an API to connect to a weather service and retrieve the current weather data for your location.

APIs are commonly used to enable different software applications to interact with each other, to create custom integrations between different software products, and to build new applications by leveraging the functionality of existing ones. APIs can be developed and published by companies, organizations, or individuals, and can be accessed through a variety of programming languages and development platforms.