Silver Proving Grounds
Tanking for Beginners: Getting started
Tanking in a massively multiplayer game like World of Warcraft is when certain classes (Monks, Death Knights, Warriors, Paladins and Druids, in the case of WoW) choose a specialization and perform a role that is intended to keep the monsters in a dungeon or raid focused on said tank, and not instead on the healers or damage dealers in the group. You may already have known that, but it can be useful to establish basics right up front.