For 1 and 1/2 year i'm playing WoW and i'm impressed with the language extensions that players have invent in order to express more effectively during the game. Each language has its own of course and i will provide a few:
Tank Usually referred to a warrior, paladin (protection) or druid (feral). The player that will face the enemy in melee combat and usually gets lots of damage.
Healadin or Spelladin A holy paladin
n00b An amateur player
Retradin A retribution paladin
Cookie cutter An Arms warrior with two-handed weapon
Off-tank Secondary tank for a party. Usually helps the tanking
DPS or DeePeeEss Damage per Second. Usually used as "ok <player>, now go dps".
Ress & ressing Ressurecting a dead player
lewt loot ... spoils from battles
mkay Okay
HoT and DoT Referred to spells or buffs that do Healing over Time, Damage over Time
Rep Reputation (usually with some in game factions)
Instance Referred when a player wants to do (or is inside) a dungeon
You can find some more slang in this web site.