The number of possible orientations, calculated as 2S + 1, of the spin angular momentum corresponding to a given total spin quantum number (S), for the same spatial electronic wavefunction. A state of singlet multiplicity has S = 0 and 2S + 1 = 1. A doublet state has S = 1 2, 2S + 1 = 2, etc. Note that when S > L (the total orbital angular momentum possible) there are only 2L + 1 orientations of total angular momentum possible.
PAC, 1996, 68, 2223. 'Glossary of terms used in photochemistry (IUPAC Recommendations 1996)' on page 2255 (https://doi.org/10.1351/pac199668122223)