application programming interface (API) A set of routines, including functions, methods, and procedures, that exposes application functionality to support integration and extend applications. Related terms application, function, method, procedure Contrast with Actuate BIRT Spreadsheet Engine, Actuate Information Delivery API (IDAPI), Actuate iPortal Security Extension (IPSE), Actuate Online Archive Driver API, Actuate Report Server Security Extension (RSSE), converter