A mobile application programming interface (API) is a set of protocols and tools that allows developers to build and integrate mobile applications with external services or platforms. It defines the methods and data formats that applications can use for communication, enabling functionalities like retrieving user data, sending messages, or integrating payment systems. Mobile APIs facilitate interoperability between different systems, enhancing app capabilities while streamlining development processes. They are crucial in creating feature-rich mobile applications in today's digital landscape.