An application program interface (API) is a set of protocols, routines, and tools for building software and applications. It specifies how software components should interact and allows them to communicate with each other.
APIs are often used to allow different applications to communicate with each other and share data. For example, a weather app might use an API to access current weather data from a weather service provider. The API specifies the way that the weather app can request the data, as well as the format in which the data will be returned.
APIs can be open, meaning that they are available to any developer who wants to use them, or they can be private, meaning that they are only available to developers who have been granted access by the owner of the API.
APIs are a key component of modern software development, as they allow developers to easily integrate different software components and build more complex and powerful applications.