And what does Ladder Decay mean? Some kind of reset?
Well, basically it should mean that player's rank is decreasing through time, when he's inactive. This is to make rankings fresh all the time, resulting in (hopefully) forcing top players to be active again, as well as giving a chance to those wannabes who normally couldn't be on the top cause some top players could've just safely stopped playing after reaching very high streak/ratio, not willing to risk it.
I hope we'll get some details on how this mechanism exactly works.