In a scientific context, what would be the best term to use when referring to the measurement of an object's matter?

The best term to use when referring to the measurement of an object's matter is mass. Mass is a fundamental property of matter that quantifies the amount of substance in an object, regardless of its location and the effects of gravity. It is typically measured in units such as grams or kilograms. Mass remains constant no matter where the object is in the universe, which is an important distinction for scientific measurements.

In contrast, weight is the force exerted by gravity on that mass, which can vary depending on the gravitational field (for example, on the Moon versus Earth). Volume refers to the amount of space an object occupies, but it does not directly measure the quantity of matter itself. Density is a derived property that relates mass to volume (density = mass/volume), but it does not measure matter independently. Therefore, mass is the most accurate term for quantifying an object's matter in a scientific context.