Class characteristics, I am unsure if many people will understand it so I will explain.
Class characteristics means the specific traits of your class, in WoW currently only your abilities, resource system, talents, stats and armor/weapons makes your class different from the other class. When it comes to the Death Knight also appearance makes it different from other classes (talking about the glowing blue eyes and the undead skin), now in end TBC a friend of mine told me that Blizzard was busy working on this difference for every class, alas only the Death Knight got a different appearance because of class choice but I do understand that.
What do you gents/ladies think of the concept that your character not only looks different because of gear and race choice but also looks different because of the class you choose. I personally think it would be awesome really, I mean imagine your warlock getting demonic runes on his face and body just because he is an warlock or a druid that has an a bit of an green aura around him and small plants growing on his or her body, those 2 examples are of course raw concepts.
Now you can of course take the concept even further and then it would be specc characteristics, currently the only specc that has that is the shadow priest because of change of appearance he or she makes because of shadowform but I personally think that more classes should at least get a signature look beside just gear. So feel free to discuss this and give your opinion.