Final answer:
A FAULT light on the TERR pushbutton of the GPWS panel indicates a Fault in the terrain database (Option A).
Step-by-step explanation:
A FAULT light on the TERR pushbutton of the GPWS panel indicates a fault in the terrain database, which is crucial for the Ground Proximity Warning System to prevent potential collisions with terrain. The Ground Proximity Warning System (GPWS) uses this database to warn pilots of potential terrain conflicts that could lead to a collision.
If there is a fault in the system, it can compromise the safety features of the GPWS. The TERR fault does not indicate issues with the aircraft's landing gear, the overall GPWS functionality, or the weather radar system. Pilots are trained to perform the appropriate checklists and procedures if such a fault is indicated.
Thus, the correct option is A.