I see a little star next to someone’s name, hovering over it shows they are a “Premium User”, what does this mean?
Ha…,! You’re talking to the boss of the site.
The genius who made this site possible.
Send him a contribution, or buy him a beer.
Without him you wouldn´t be here.
Just fooling, don’t care.
Welcome, and enjoy the site!
Cheers!
As Madfox implies, those are site admins.
I also recommend donating to the site, as I’ve done, to help keep it running, if you use it a lot… you won’t get a special badge, though. 
Only Quaddicted staff get that meaningless fancy star 