A component, \(M_{S}\), of the angular spin moment \(S\) along an arbitrary axis (usually chosen as the z-direction). \(M_{S}\) can take the values between \(-S\) and \(S\): \(-S\), \(-S+1\),..., \(S- 1\), \(S\). The term is also used to denote an operation (spin-symmetry projection) allowing one to eliminate @ST07103@ in the cases where wavefunctions are not eigenfunctions of the operator \(S^{2}\).