What distinguishes mass from weight ?

 Mass is constant and does not depend on gravity, Where As Weight is the force something exerts from its acceleration due to gravity.

Example: A 100 g sample is 100 g on the earth, on the moon, wherever. Since the force of gravity varies, this amount can vary greatly depending on where the thing was weighed. Even on earth the difference in the force of gravity between different elevations is sufficient for an object's weight to be different.