I had to have my friend explain it all to me. He's into WoW. Here's what I got out of it:
Whelp: A baby dragon; there are many along the outside edge of the dungeon that is featured in this video
Agro: How much the boss hates you. The more it is, the more dmg you take. I assume they try to balance Agro between everyone.
DPS: Damage Per Second
Dots: Damage Over Time Spells
DKP: Dragon Kill Points; guild system of keeping track of how much you help. Not a feature of the game itself.
Tail: Onyxia is a dragon boss, and he does a tail whip that shoves you into the Whelps. When that happens, a bunch of whelps come after you and your party and you get butt-forked from behind.
Wipe: When everyone in the group dies
fork: This guy's favorite word