Fantastic guide Op!
It's very straightforward, and wets teh "tongue" so to speak on grouping
I think it fills that role quite well. You could probably add a few more things in it and still keep it simple (which is probably your main goal).
On threat - As stated earlier, the clarification between threat (what the mob builds), and Aggro (when you have enough threat for the mob to want to whack you instead of the others), are two different things. easy to throw in there though.
On roles - I'd add the definition of DPS to your DPS description (which is otherwise great). It may be helpful for new players to know that it mean Damage Per Second. initially it was simply a way to determine how much damage your class was doing...but it quickly became an industry standard for defining the classes (and SPECS !!) that focus solely on dishing out the mayhem.
Plus, theres a few other things that I think , while still keeping things very basic, will help out a ton.
1) Marking - Sometimes a group member will put little markers above the heads of various mobs. These are often used to differentiate things like Kill order, who to CC (more on CC below), and in general...gives you a way of organizing that mess of uglies standing between you and that sweet phatz lewtz! If the person marking doesn't explain what each marker means at the start, you may want to ask. Often they will use the same markers for the same things, such as "kill the target reticule first, then the flame, then the blue shield, " etc. But for the most part, if a tank or healer marks mobs, they will tell you what their for. Learning to follow markers makes huge waves with other players, well worth the little extra focus it takes to keep track of them.
2) Crowd Control - or "You want me to do WHAT to that monster?"
As you level, you'll notice that your class (or classes, if you play a dozen or so like I do) will have a few skills that allow you to control mobs without having to damage them. sometimes you shock them, sometimes you stun them, or put them to sleep, or scare the wits out of them...each class has their own ways of Controlling a mob. It can help out a bit when your playing solo, but in a group they can become critical survival tools.
So when you get into a group, and someone asks kindly if the "Sorc can CC the mob with the Blue shield above his head", DONT PANIC! this is very normal. What they mean is they want you to use your "stunning" ability, which is often called CC, or Crowd Control. But keep in mind that they usually mean the long one...the classes that are known for their CC abilities will usually have a LONG CC (lasts 1 minute with a 45s-1m cooldown usually), and a SHORT CC (instant, but only works for a few seconds). save your short CC for surprises...use your long one when they ask you to CC.
But keep in mind that the job isn't done. once that mob is CC'ed, you need to watch it. the group expects you to continue to CC it (recast it when its CD is up) until they all eventually run over to give that Mob a smacking. so don't let it out of your sight. It feels like allot to do initially, but don't be worried. after a bit watching your CC becomes second nature.
4) Mob - usually refers to a single enemy. Originated from older MMO's where enemies would hang out in groups, or "mobs" of enemies (loose origination...there are a few variations of where it comes from). You'll hear this allot in groups. "hey Sorc, can you CC that Mob on the left?" Mob = 1 enemy. Mobs = more then one.
5) AoE - Nope it doesn't mean that the group is All Over Everything
it's an acronym that means "Area Of Effect", and is used to describe spells that do damage to areas, able to hit many Mob's at once. They may do it in a circle, or they may do it in a cone shape in front of your character. Some may be centered where you want them to be (targeting the ground), some may be targeting a specific Mob, and hits the mobs around it. Doesn't matter really.
What you need to know is sometimes the group may not want anyone to "AoE this pull". It's usually because they are using CC on various mobs, and they don't want the CC to "break", in which case the mobs that was CC'ed will usually turn and attack the HEALER (this is bad. especially if your the healer). so pay particular attention to the group your fighting. If there's any that are controlled, don't use your AoE attacks.
Oh yeah...and avoid the bad stuff. May be Red, May be green, May Glow, may ask you if you want a drink...if its on the ground and the enemies put it there, for the most part its BAD and you should MOVE OUT OF IT. hopefully fast. Even if its not bad, moving out of something your not sure about is a good thing to do. Unless its your healers Kolto missle....but they'll chuckle at ya, and you'll figure it out fast