An API allows separate software systems to communicate and work together. It acts as a messenger that runs between applications, databases, and devices, using standardized programming instructions. APIs enable one software system to use services from another system. For example, the Uber app uses the Google Maps API to display maps. APIs help developers build new services faster by leveraging existing capabilities rather than reinventing the wheel. They can speed up development time, improve customer experience through flexibility and customization, and enable innovation through partnerships.