Center of gravity (CG)
The point at which the mass of the aircraft would be balanced if it were placed on that single point. The point changes depending on the loading of the aircraft: fuel, passengers, luggage, etc. Each aircraft has CG limits specified by its manufacturer. If the CG of the aircraft in its current configuration is outside of the specified limits, the aircraft may be unsafe to fly as the control surfaces will have insufficient authority to safely control the aircraft. For example, if the CG is behind the aft (rear) CG limit, the aircraft will tend to stall.
