A static external magnetic field exerts a force on magnetic moment which is equal to negative gradient of the potential, that is the definition of the potential in electrodynamics. However, the physical meaning of the potential is not given by this definition. We will discuss the physical content of the potential, showing that the potential of a macroscopic magnetic moment and magnetic field-depending energy of an atom are different in physics, although they have the same expression. The one for the atom is part of the internal energy of the atom.