Mass is a measure of how much matter there is in an object.

In our daily lives, the terms mass and weight are virtually interchangable. But, in reality, they are not the same thing. The weight of an object on the moon is less than it is on Earth; and in space, the same object is weightless. The mass of the object does not change, regardless of where it is.

Weight is a measure comprised of a combination of the mass of an object and the pull of gravity on that mass.

In the SI system of units, the units of mass include grams (g) and kilograms (kg). In the Imperial system of units, the units of mass include pounds (lb), ounces (oz), slugs, and tons (t).