I know these prefixes:
[table="width: 500"]
[tr]
[td]g [/td]
[td]game (server side VM)[/td]
[/tr]
[tr]
[td]cg[/td]
[td]c(lient )game (client side VM)[/td]
[/tr]
[tr]
[td]ui[/td]
[td]user interface VM[/td]
[/tr]
[tr]
[td]bg[/td]
[td]both "games" (actually all three VM's: g, cg, ui)[/td]
[/tr]
[tr]
[td]sv[/td]
[td]server[/td]
[/tr]
[tr]
[td]cl[/td]
[td]client[/td]
[/tr]
[tr]
[td]snd[/td]
[td]sound[/td]
[/tr]
[tr]
[td]tr[/td]
[td]renderer (don't know what it stands for, cvar prefix is just »r«)[/td]
[/tr]
[tr]
[td]bot[/td]
[td]I'm not telling[/td]
[/tr]
[/table]
I assume they are used to fake namsepaces.