CHARMM Development Project Forums CHARMM Interfaces CHARMM-GUI Meaning of BB and SC in DPOSRES_FC_

What do the terms "BB" and "SC" stand for in "-DPOSRES_FC_BB" and "-DPOSRES_FC_SC" in the define constraints line in mdp files downloaded for GROMACS from CHARMM-GUI Input Generator?

I believe now that BB stands for Backbone and SC stands for side chains. Both referring to a protein in the system and the constraint command is present in the mdp files whether there is an actual protein in the system or not.
Hope this is helpful.