Azimutal quantum number denotes the angular momentum associated with the orbital of rotation of electrons around the nucleus. Angular momentum of electrons are involved in calculation of this energy. That is why it is called angular quantum number. It is the secondary quantum number, after the principal quantum number.
the angular momentum (linear momentum* distance from nucleus) is expressed as a number m = 0, 1, 2, 3.. as the actual angular momentum is a multiple of that for m=1