OK... I've never looked it up before.... don't know why... but this is what Wikipedia had to say about online trolling....

In Internet slang, a troll [[/ˈtroʊl/, /ˈtrɒl/) is a person who sows discord on the Internet by starting arguments or upsetting people, by posting inflammatory, extraneous, or off-topic messages in an online community [[such as a newsgroup, forum, chat room, or blog) with the deliberate intent of provoking readers into an emotional response or of otherwise disrupting normal on-topic discussion.