Its a common Internet term on most forums that refers to someone that goes into the forum to disrupt or disturb others with outrageous comments for no more than the fun of causing a flame war.
Usage:
Application of the term troll is highly subjective. Some readers may characterize a post as trolling, while others may regard the same post as a legitimate contribution to the discussion, even if controversial. The term is often used as an ad hominem strategy to discredit an opposing position by attacking its proponent.
Often, calling someone a troll makes assumptions about a writer's motives. Regardless of the circumstances, controversial posts may attract a particularly strong response from those unfamiliar with the robust dialogue found in some online, rather than physical, communities. Experienced participants in online forums know that the most effective way to discourage a troll is usually to ignore him or her, because responding tends to encourage trolls to continue disruptive posts — hence the often-seen warning: "Please do not feed the trolls".