1) The state of being multiple, made of several components.
2) In atomic and nuclear physics, the number of → levels
into which the energy of an atom, molecule, or nucleus splits as a result of
→ Russell-Saunders coupling between
→ orbital angular momentum and
→ spin angular momentum. It is given
by 2S+1, where S is the total electron
→ spin quantum number.
The multiplicity of an energy level is indicated by a left superscript to
the value of L, where L is the resultant electron orbital angular
momentum of the individual electron orbital angular momenta.
3) In → statistical mechanics,
the number of → microstates corresponding to a given
→ multiple; → -ity.