Definition - self centered, egotistical leeches that thirst for rage.

Characteristics:
-Mostly child-like in nature (ex. poor grammar, spelling and narrow-minded posts), Trolls may be as they seem, or simply using this childish disguise to provoke more rage.
-Comments are blatantly obvious for the most part, usually sporting a phrase completely opposite of what you'd expect
-Usernames reflecting common annoyances in today's internet culture (ex. "troll3r", "Umadbr0", "l0lf4gz", "itr0llu")
-Not all trolls exist to start an internet riot, a lot of them wait to tear down another users post in hopes of encouraging rage. (ex. "Nice spelling Noob, you obviously are retarded")

Trolls can be good or bad.

Good Troll - "Megadeth Sucks!!" on a Megadeth music video comment section. Obviously a light hearted attempt to enrage people who can't take an obvious joke,

Bad Troll - "Megadeth is overrated, Mustaine is a coward, a poor guitar player and an egotistical pussy. They have yet to gain any fanbase or sell any decent records in decades...sellouts." This is obviously a Troll Comment whose entire purpose is to spark a rage war among every viewer of said video.

someone who trolls youtube comments, usually by saying something controversial or that will piss people off. these can be found at the comments section on a youtube video.(duh). most commonly trolled videos are Metal music videos,obama speeches. ones that trolls metal videos often have a screen name like "justinbeibergirl" or "disneyrox12".people who rely on the anomimity of the internet. people who no one gives a shit about so they piss people off over the computer.