MTOW — maximum take-off weight

MTOW is the greatest weight at which an aircraft is certified to begin its take-off roll: the airframe, the fuel, the passengers, the cargo — everything, all at once. It is not a measure of how much the aircraft weighs. It is a measure of how much it can lift.

It matters because almost every other limit follows from it. Fuel and payload compete for the same allowance, which is why a fully loaded aircraft cannot also carry full tanks. It sets the runway length required, the landing fees an airline pays, and which airports the aircraft can use at all.

It is also the honest way to rank aircraft by size. Length flatters slim aircraft and wingspan flatters gliding efficiency, but MTOW measures raw lifting power — which is why the An-225, at 640 tonnes, sits alone at the top of the board.