An API (Application Programming Interface) is a set of rules and protocols that allows different software applications to communicate and share data with each other. APIs define how requests for data or functionality should be made, specifying the format for inputs and outputs. In web development, APIs often enable interactions between a client (like a website or mobile app) and a server, allowing the client to retrieve or update information without directly accessing the server’s internal processes. Examples include APIs for accessing data from a weather service, social media platforms, or payment processors.