I always felt that true definition of a troll is someone who is intentionally provocative with no purpose other than to inflame members...the name comes from "trolling"...dragging your bait from a boat to catch a fish. To me, the term is applied too often to members who are just jerks.
Someone who injects absolutely nothing of substance into a thread. Generally just behaves like an a$$.
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,[1] 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[2] or of otherwise disrupting normal on-topic discussion.[3]