I'm new to MMO's with my only experience being with DC Universe Online. On that game, the descriptions are pretty cut and dry. You are either a healer, tank, or controller. Everyone can be DPS as long as you run in that stance and have the appropriate equipment on. But I know what role is what there:
Fire/Ice/Earth/Rage = Tanks
Mental/Gadgets/Hard Light/Quantum = Controllers
Sorcery/Nature/Electricity/Celestial = Healers
And as I said, you can run all as DPS as long as you do your powers and equipment properly. Now, for here, I think I understand that Priests are healers but what roles are tanks, controllers(support), and exclusively DPS?