Weight is the measure of the heaviness of an object. While weight is proportional to an object's mass, the terms mass and weight are slightly different.
The dictionary defines weight, in addition to being an object's heaviness, as "the force with which a body is attracted to Earth or another celestial body, equal to the product of the object's mass and the acceleration of gravity." Whereas mass is a measurement of the amount of matter in an object, an object's weight is proportional to both its mass and the gravitational acceleration applied to the object. For example, if two identical objects were on Earth and the moon respectively, the objects would have the same mass, but the object on the moon would have less weight. This is because the gravitational force of the moon on an object is less than that of the Earth.