Microwave "power" vs "power consumption"
The 1440 W power consumption is what you can expect to supply from the 120V outlet. That supplies 1100 watts to cook the food and 340 watts of losses inside the microwave including power for the turntable motor, the controls, the heat produced by the transformer, microwave generator and associated circuitry and the motor that drives the fan to push the heat out into the room.