spin projection

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 spin contamination in the cases where wavefunctions are not eigenfunctions of the operator S 2.
PAC, 1999, 71, 1919. 'Glossary of terms used in theoretical organic chemistry' on page 1963 (https://doi.org/10.1351/pac199971101919)