Checked out a couple of FMC Supplementary Data documents, (B772/ B744/ B74C) they refer to VG as the "Ground Speed". Vmin is also defined as "Minimum Speed".
Putting the two of these together gives you the "Minimum Ground Speed", but i cant find that exact definition.
It should be noted that the VG speed is distinct from the VMCG speed and is used for cruise/holding calculations.
Mutt.