An Application Programming Interface (API) is a set of rules and protocols that allows different software applications to communicate with each other. APIs define the methods and data formats that applications can use to request and exchange information, making it easier for developers to integrate different services and functionalities into their own applications. For example, when you use a social media app to share a photo, the app uses an API to send the image to the server of the social media platform, like Facebook or Twitter. This process allows developers to build on existing platforms without having to create everything from scratch, promoting innovation and efficiency in software development.