Center of gravity (CG)

The location on an aircraft about which the force of gravity is concentrated.

Aviation Maintenance Technician Handbook — Airframe, p. G-7

(GAMA) The point at which an airplane would balance if suspended. Its distance from the reference datum is determined by dividing the total moment by the total weight of the airplane. It is the mass center of the aircraft, or the theoretical point at which the entire weight of the aircraft is assumed to be concentrated. It may be expressed in percent of MAC (mean aerodynamic cord) or in inches from the reference datum.

Aircraft Weight and Balance Handbook, p. G-2

The theoretical point where the entire weight of the helicopter is considered to be concentrated.

Helicopter Flying Handbook, p. G-2

The point at which an airplane would balance if it were possible to suspend it at that point. It is the mass center of the airplane, or the theoretical point at which the entire weight of the airplane is assumed to be concentrated. It may be expressed in inches from the reference datum, or in percentage of mean aerodynamic chord (MAC). The location depends on the distribution of weight in the airplane.

Pilot's Handbook of Aeronautical Knowledge, p. G-6