Trolling is a kind of prank and a lost art form, full of failed attempts and people who don't even know what trolling is.
Most ignorant newfags think that trolling is merely someone getting in an argument, or a fight, or attacking others. However, people do this all the time on the internet when they're not trolling. Trolling that does this is obvious and usually fails. People who think everyone who disagrees with them is a troll are so easily trolled that they'll fall for Concerned Mother. A skilled troll can just appear to cause no conflict and agree with people and do it in such a way to provoke everyone else into a shitstorm.
A troll, most commonly encountered on the internet, is any person who purposely causes controversy in a web community and disrupts shit for his own amusement. Trolls have been refered to in the web community as, trollers, assholes, jerks, and scum of the earth douchebags. The term probably derives from "trolling" or "trawling", a style of fishing which involves trailing bait through a likely spot hoping for a bite. Troll is fine as a verb since trawling/trolling for comments and flames is innate troll behavior. Trolling is not to be confused with the gay slang verb "to troll", which means to trawl for anal sex, unless of course it's done by Perverted Justice.