Plain English Meaning
The controller who tells you how to taxi around the airport — between the ramp and the runway — but doesn't handle takeoffs or landings.
Full Definition
The ATC (air traffic control) position responsible for directing the movement of aircraft and vehicles on the airport's taxiways and other non-runway movement areas. Ground Control issues taxi instructions and clearances between the parking area and the runway, but is not responsible for takeoff, landing, or runway operations, which are handled by the tower controller.