$^{2S+1}L_J$ was the term symbol.

I watched a video online saying $2J+1$ was the fold of degeneracy to the term symbol.

Specifically, for nitrogen, the term symbol for the lowest energy was $^4S_{3/2}$ which means it has 4 fold degeneracy. But I couldn't figure out how this could be as all the electron are at spin up states, and there's only 3 orbit in $2p$ shell.

Further, what's the meaning of multiplicity $2S+1$ mean here?