An Application Programming Interface (API) is a set of rules and protocols that allows different software applications to communicate with each other. It defines 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. APIs are commonly used in web development, enabling applications to access features or data from other services, such as social media platforms like Facebook or Twitter. By using APIs, developers can create more complex applications without having to build every component from scratch, saving time and resources.