Threat - Threat is what causes a creature to attack a target. The Tank needs to generate enough threat to keep the Mobs / Boss attacking him. DPS also need to make sure they do not exceed the Tanks threat on the target. Example: I am a DPS, who is new. I cast lots of high threat spells during a Boss fight. The Boss turns around and kills me because I had more threat than the Tank. Since no one else had more Threat than the Tank the Boss re-focuses of him again. And I have to sit down and watch everyone fighting because I am dead.