An Application Programming Interface (API) is a set of protocols, tools, and definitions for building software and applications. It specifies how software components should interact, allowing different programs to communicate with each other. APIs are used to enable the integration of new features, data sharing, and interaction between different software systems. They play a crucial role in modern software development by simplifying the programming process and enabling seamless connectivity between different services and platforms. Common uses of APIs include connecting web applications to databases, enabling communication between software products, and facilitating third-party service integrations.