Final answer:
Greenwich Mean Time (GMT) refers to the time at the prime meridian in Greenwich, England.
Step-by-step explanation:
Greenwich Mean Time (GMT) refers to c) the time at the prime meridian. GMT is the time zone that is based on the local time at 0 degrees longitude, which is the prime meridian located in Greenwich, England.
It is used as a reference for coordinating international activities and is the standard time for many purposes such as military operations, international radio broadcasts, and air traffic control systems.