Plain English Meaning
The total stress the wings are carrying during a maneuver, measured as how many times the airplane's normal weight they are holding up at that moment.
Full Definition
The total load factor produced when an airplane is simultaneously supporting its own weight and generating the additional lift required to perform a maneuver, such as a level turn or pull-up. It is the combined effect of the gravitational load (1 G) and the centripetal load created by the maneuver, expressed as a multiple of the airplane's weight.
Context Anchor
Seen when learning how the airplane feels in turns, especially why a steeper bank makes the airplane feel heavier and requires more support.