The scientific word that describes how much stuff is in an object is mass.

Here's why:

* Mass is a fundamental property of matter that measures its resistance to acceleration. It's essentially a measure of the amount of matter an object contains.

* Weight, on the other hand, is the force of gravity acting on an object's mass. It can change depending on the gravitational field.

So, while we often use the terms "weight" and "mass" interchangeably in everyday language, in science, they have distinct meanings.