Final answer:
A FAULT light in the ADR pushbuttons of an ADIRS panel indicates a problem with the Air Data Reference System.
Step-by-step explanation:
In an ADIRS panel, a FAULT light in the ADR pushbuttons indicates an error or malfunction in the Air Data Reference System. The Air Data Reference System is responsible for providing crucial data to the aircraft's navigation and flight control systems, such as airspeed, altitude, and vertical speed. When the FAULT light is illuminated, it signifies that there is a problem with one of the ADR units, and it needs to be addressed by maintenance personnel.