When I'm writing a scenario, the pivotal scene isn't usually based on the toughest opponent, but on the most important objective. That may or may not involve a tough bad guy, but if it does, I'm typically just as happy if my players find a way to go around it or otherwise achieve the objective while avoiding a risky "boss fight."

And of course, there's the problem that my players tend to very quickly neutralize the uber-tough opponents (usually several scenes before they were even supposed to have the fight) and then get their heads handed to them by what was supposed to be a chump. Powerful evil wizard? No problem. Pair of low level orc flunkies? Two dead PCs. (Made worse because that was only the second scenario of the campaign. I handwaved it to let the PCs survive with serious injuries instead of dying.)

The thing about tabletop games, though, is that every writer wants to be unique. It's a hobby filled full of people who see the way "everyone else" does it and then decide to go a totally different direction (with varying results). So outside of the more formal D&D School, I'd be rather surprised if gamers managed to agree on any particular designation for particular kinds of opponents.

And speaking of D&D, 4e's DM Guide did offer up a list of monster roles: Brute, Controller, Lurker, Soldier, Leader, Artillery, Skirmisher, Solo… There may be one or two others; I don't recall. The "Solo" monster is roughly equivalent to a boss in that it's supposed to be as tough as five ordinary monsters, but that's because it usually shows up alone and still needs to be threatening to a group of PCs. Those roles serve as a way of more easily discussing and planning encounters formally.

In your own planning, and even in communicating with your group, whatever parlance you find most comfortable and useful is the one you should use. It's true that many gamers frown on video game jargon entering tabletop gaming, but speaking solely for myself, I also cannot stand to see people use the word "toon" in reference to their character in EVE Online. It totally ruins my sense of immersion to have such metagame ideas intrude into my roleplaying. My viewpoint is my own, though, and you shouldn't let it ruin things for you. If you want to use terms like "mob" and "aggro" in your games, then do it! Don't let us sticks in the mud cramp your style!