Troll Definition from Jargon File
The following is from the Jargon File, found at [ http://www.tuxedo.org/~esr/jargon/html/entry/troll.html ] , 2003. —Xah Lee
1. v.,n. [From the Usenet group alt.folklore.urban] To utter a posting on Usenet designed to attract predictable responses or flames; or, the post itself. Derives from the phrase “trolling for newbies” which in turn comes from mainstream “trolling”, a style of fishing in which one trails bait through a likely spot hoping for a bite. The well-constructed troll is a post that induces lots of newbies and flamers to make themselves look even more clueless than they already do, while subtly conveying to the more savvy and experienced that it is in fact a deliberate troll. If you don't fall for the joke, you get to be in on it. See also YHBT.
2. n. An individual who chronically trolls in sense 1; regularly posts specious arguments, flames or personal attacks to a newsgroup, discussion list, or in email for no other purpose than to annoy someone or disrupt a discussion. Trolls are recognizable by the fact that they have no real interest in learning about the topic at hand - they simply want to utter flame bait. Like the ugly creatures they are named after, they exhibit no redeeming characteristics, and as such, they are recognized as a lower form of life on the net, as in, “Oh, ignore him, he's just a troll.” Compare kook.
3. n. [Berkeley] Computer lab monitor. A popular campus job for CS students. Duties include helping newbies and ensuring that lab policies are followed. Probably so-called because it involves lurking in dark cavelike corners.
Some people claim that the troll (sense 1) is properly a narrower category than flame bait, that a troll is categorized by containing some assertion that is wrong but not overtly controversial. See also Troll-O-Meter.
The use of “troll” in either sense is a live metaphor that readily produces elaborations and combining forms. For example, one not infrequently sees the warning “Do not feed the troll” as part of a followup to troll postings.