An API, or Application Programming Interface, is like a digital bridge between two systems, permitting bidirectional communication. One computer (usually in a firm) makes an API call, and another computer (usually a data vendor) responds by providing raw data. Through APIs, developers can interoperate with functions and data from other software or databases — without having direct access to those external systems’ internal code. Essentially, APIs provide the methods and data formats that applications can use to request and share information.