Plain English Meaning
The single balance point of the airplane — the spot where its weight is effectively centered. Where this point sits (further forward or further aft) changes how the airplane handles.
Full Definition
The point on an airplane at which all of its weight is considered to be concentrated and balanced. It is the theoretical point around which the aircraft would balance if suspended, and it is the point about which the airplane pitches, rolls, and yaws in flight.
Context Anchor
Seen in weight-and-balance calculations, aircraft loading, and stall discussions where airplane handling and recovery are affected by loading.
Derivation
From Latin gravitas, meaning weight or heaviness. The 'center of gravity' is literally the center of an object's weight — the one point that represents where all the weight effectively acts.