What is this Troll thing?

I keep seeing people use it while answering questions.



Thanks
In Internet slang, a troll is someone who posts inflammatory, extraneous, 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 a desired emotional response[1] or of otherwise disrupting normal on-topic discussion.[2] In addition to the offending poster, the noun troll can also refer to the provocative message itself, as in that was an excellent troll you posted. While the term troll and its associated action, trolling, are primarily associated with Internet discourse, media attention in recent years has made such labels highly subjective, with