Rubber-banding is a form of latency lag. You will run 10 meters ahead and instead of your screen freezing or your character running on the spot, your character gets teleported back to your original location, in severe cases your character gets jerked ahead and back again simulating the "Rubber-Banding" effect. *edit* As an aside, Aion had it the worst, was freaking terrible and completely un-playable for many players.