Atomic term (${}^{2S+1}L$)

An LS coupling multiplet with specified total orbital angular momentum $L$ and total spin $S$, usually within a specified electron configuration. Its magnetic states have $M_L=-L,\dots ,L$ and $M_S=-S,\dots ,S$. Spin-orbit coupling splits it into atomic fine-structure levels.

An atomic term with total spin one half and spin multiplicity two. A doublet S term has only J=1/2, while a doublet with nonzero L can have J=L-1/2 and J=L+1/2. Spin multiplicity therefore need not equal the number of resolved spectral lines.

A level of an atomic term with specified total angular momentum $J$. Without an external field, its $2J+1$ magnetic states remain degenerate in a rotationally invariant Hamiltonian.