An "API," or Application Programming Interface, is a set of rules, protocols, and tools that allows different software applications or systems to communicate and interact with each other. It defines the methods and data formats that applications can use to request and exchange information or functionality. APIs enable developers to access and utilize specific features or data from one application or service in another, without needing to understand the internal workings of the systems involved. This interoperability and data exchange are crucial in today's software development, as they allow for the integration of various services and functionalities to create more powerful and versatile applications. APIs are used in a wide range of contexts, from web development and mobile apps to hardware and software integration.