Mass is a measure of how much matter an object has. Weight is a measure of how strongly gravity pulls on that matter. Thus if you were to travel to the moon your weight would change because the pull of gravity is weaker there than on Earth but, your mass would stay the same because you are still made up of the same amount of matter.
Answered by: A. Godbehere, High School Student, Port Perry
Imagine yourself out is space away from any gravitational field, with a bowling ball in your hands. Let it go and it just floats in front of you. Without gravity, it has no weight. Now grab it again and shake it back and forth. That resistance to being moved is inertia, and mass measures how much inertia an object has. Inertia does NOT depend on gravity.
Mass is determined only by the amount of matter contained in an object.
Any two masses exert a mutual attractive force on each other. The amount of that force is weight. A one kilogram mass on the Earth's surface results in 2.2 pounds of force between the mass and the Earth, so we say the mass weighs 2.2 pounds. That same one kilogram mass on the Moon, because of the Moon's lower mass, results in only about 1/3 pounds of mutual force.
Just remember that the weight of an object depends on where it is, while its mass stays the same.