If you're playing on live servers you probably know what Fade is by now (hopefully)! It's the ability that most classes have which has a chance to instantly clear your agro and drop you from combat. Still confused? The screen shot below is of the Mage Fade ability, Drape of Shadows.
Almost every class gets a Fade ability - some of them are great and instant cast but other classes get reemed in the butt and their fades kinda suck... Clerics and Warriors are who I am thinking of in this case. Even worse - Shamans have a fade that turns them into a totem pole and roots them/makes them unable to take action for like 30 seconds.
One really important piece of advice that I can think to give you about Fade is do not bind your Warrior/Tanks Fade to your fade key!!! Your fade key is primarily going to be used when your group pulls agro and you need to save their lives. Fading on your Warrior at this time will only make things worse since he'll lose any agro he had in the first place.
Mage: Drape of Shadows
Wizard: A Hole in Space
Warrior: Howl of the Warlord (DO NOT BIND THIS FADE TO THE SAME KEY)
Enchanter: Self Stasis
Bard: Fading Memories