An API (application programming interface) is a set of rules and protocols that allows different software applications to communicate and share information with each other. It acts as a bridge, enabling one application to request data or services from another, which is crucial for integrating various systems and platforms. APIs are widely used in web development, allowing developers to access external data, features, or services, such as payment gateways, social media platforms, or third-party tools. By facilitating seamless interaction between applications, APIs help streamline processes, improve functionality, and enhance the user experience across digital platforms.