butremor :
It was mentioned on this page http://www.tomshardware.com/reviews/gaming-graphics-card-review,3107.html
In that specific case it's talking about GHz edition vs. non-GHz edition.
AMD makes two models of each card - one at normal clocked, and one pre-overclocked to around 1GHz.
Vanilla, obviously, is the stock-clocked 7870.