Potential energy is energy that can be considered as "stored" in an arbitrary object. It can be computed as the product of the mass of the object, the acceleration due to gravity, and the height from a reference level. The reference level is arbitrary. Drag any one of the several objects from daily life to see the change in its potential energy. The two reference levels chosen are the floor and the surface of the table. Only the difference in potential energy is relevant, which is why the choice of reference level is arbitrary.