What's the background I need to know to understand the conjectural

     D (Bun_G)  =?=  O(LocSys)

from [this question][1]. I know the LHS is about the derived category of D-modules on the space (stack?) of some (stable?) bundles for some preselected group G. What's the RHS? I've seen the physics articles that say something about his topic, but how would you explain it?

I know this goes under the name of Geometric Langlands. Why?


  [1]: http://mathoverflow.net/questions/2464/what-is-drinfelds-manuscript-best-dream-in-russian-about