Plain English Meaning
The heaviest the airplane is allowed to be when loaded up and ready to fly. Anything heavier than this number is not legal and not safe.
Full Definition
The highest total weight at which an airplane is approved to operate, as established by the manufacturer and published in the airplane's type certificate and Pilot's Operating Handbook. It includes the empty weight of the aircraft plus all fuel, oil, occupants, baggage, and cargo. Operating above this weight is prohibited and degrades performance, structural margins, and stall behavior.
Context Anchor
Used in weight-and-balance, performance, and stall-speed discussions, especially when comparing the airplane’s actual with its approved limit.