Plain English Meaning
A button the pilot presses that tells the aircraft 'apply full power and climb' — used either to take off or to abandon a landing approach and climb back up.
Full Definition
TOGA is a flight mode, typically activated by a button on the throttle or thrust levers, that commands the autothrottle and flight director to apply takeoff or go-around thrust and pitch guidance. When pressed during takeoff, it sets takeoff thrust and the appropriate climb attitude. When pressed during an approach or , it commands go-around thrust and pitches the aircraft up to climb away from the approach.