Integral values between l and -l (including 0); related to the orientation of the orbital in the space relative to the other orbitals of the atom. This gives the number of possible orbitals for each sub-shell (s, p, d, or f): s can only have 1 (m_l = 0), p can have 3 (m_l = -1, 0 1), d can have 5 (m_l = -2, -1, 0, 1, 2), and f can have 7 (m_l = -3, -2, -1, 0, 1, 2, 3)