In Internet slang, a troll is someone who posts controversial, inflammatory, irrelevant or off-topic messages in an online community, such as an online discussion forum, chat room or blog, with the primary intent of provoking other users into an emotional or disciplinary response or of otherwise disrupting normal on-topic discussion.
Troll defined: (via wikipedia)
In Internet slang, a troll is someone who posts controversial, inflammatory, irrelevant or off-topic messages in an online community, such as an online discussion forum, chat room or blog, with the primary intent of provoking other users into an emotional or disciplinary response or of otherwise disrupting normal on-topic discussion.