Could someone please tell me the definition of a troll?

Pardon my ignorance but I thought a troll was a "poster" that only signed up to start talking smack or get some digs in on a specific post. Is a troll now someone who is new to the thread and questions the validity of the respondent?

EDIT: Am I trolling now?

Quote:
...excluding incidents that are misportrayed in the media, such as the Rodney King incident...


What the heck is to be misportrayed about a guy getting his head kicked in by numerous officers well after the "threat to the public" has been neutralized?


Matthew W. Campbell-- bigMoney Racing
--1999 SVT #220 "NT4UA" /O.Z. Crono Evo\'s/ /Rear Deck Sub/ --1972 Chevrolet C/10 Custom Deluxe--1980 Camaro in fewer pieces--
"If I had invested...in IBM or something like that, I would certainly have been wealthy within a decade. Instead, I bought a Porsche...and got a life" Leon Mandel