When I did my ATPL in the early 1990s, we spoke of MTOM - mass - not weight, as weight is a function of mass and gravitational force. So both from an engineering and physics perspective, speaking of mass is more accurate than weight which varies depending on your location (albeit by tiny amounts). I'm surprised to see that not a single one of you commenters here is using mass. Has this changed in the syllabi to use weight?
Again, given the basic nature of the OP's question, it did not seem worth adding extra unnecessary detail. In aeroplanes taking off from Earth, we are working against Earth's gravity, so weight is the parameter we are more concerned with. (W = mg).
If you fly into orbit, or to the Moon, then yes there will be a huge difference between mass and weight, but I would suggest that is far too much detail in the context of the question?