Someone who is purposefully posting on a forum/messageboard/site sith the sole aim to irritate the regular members.
Contrary to popular belief there is much more to internet trolling than posting "OMG UR ALL SO GHEYYYY!!!1" "OMFG TRIVIUM SUX ASS U FAGS LOL" and the like. People who post such things will usually be one-post wonders and get banned, however the more experienced troll will attempt to cause some sort of havoc under the admins radar.
Common examples of trolling:
The long-term troll:
These guys don't mind waiting around for the fun to begin. They may pretend to be an average n00b, and give themselves the stereotyical interest(s) of the average member of said forum, then once having a few posts they will gradually try to spread dissent. This type may even pretend to be pally to the admin and get their msn (and try to crack their account password of course) whilst causing general disruption. May act under other proxies and slate these fake trolls on msn to the aforementioned gullible admin. These people, to be frank, usually have no life and love bringing message boards to their knees by putting considerable time into their carnage. If they crack the admins password the board is doomed.
The sophisticated troll:
This type will usually have some sort of distaste for whatever the said message board is discussing and try to cause annoyance as opposed to destructiveness. They will parody the members and see how much they can get over their heads. Subtle pisstaking being their route. They'll usually get banned in the end but will annoy an entire community using this drawn out approach.
The faker troll:
A clever troll, the main aim of the game is to, ironically, act really REALLY stupid, this trolls aim is to argue with members incoherantly, usually using text speak. This is a ploy, the troll only needs to spend 10 seconds writing the babble when the member wastes 10 minutes writing a much more wordy reply. The troll will reply with a stupid rebuff making the member post as many long replies as possible. Using the members weight against them and wasting their forum time... If they are good then their act will be believable and they probably won't get banned unless the admin is strict on txt tlk.
The rank and file spammer:
These are the first to pop into peoples minds, they are similar to the examples stated in the first paragraph. No previous experience necessary, this lot will swarm in, again, usually under proxies to maximise the destructiveness, and spam the place to hell. Only causes mild irritation if not in large numbers.
Join any popular forum for a year and I guarantee you'll see all of these.
(let's assume it's a metal board)
Faker troll (expecting to cause irritation):
"Hi im nu here u all seem kl i am rly metal rawrrr i leik slipnot and fall out boys!!!1 they r so metal! see u al on da forum xxx"
Rank and File spammer:
"LOOOOL U METAL PPL R SO GHEY WITH UR SHOUTY MUSIC WRIST SLITTING ANIMAL FUCKING SATAN SHIIIT"
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