A troll is a common Internet term for a participant in a discussion who is saying things for the sake of getting an angry reaction from other participants or to damage the atmosphere of a community. They may do so simply by strongly and repeatedly stating an unpopular opinion in communities where they know that that subject will derail the existing topic, but they may also resort to any or all of cruelty, lies, targeting of unpopular individuals or continual obscenity in public or private messages to individuals in order to get a reaction. They may also ally with each other or create sockpuppets in order to fuel the sense that a community is being wrenched apart by dissent.
Trolls frequently, although not always, use anonymity or pseudonymity in order to not associate their nastiness with their real name, thus causing some venues to ban anonymity or pseudonymity despite their usefulness to genuine participants in forums.
Some comments on geek feminism incidents appear to be from trolls, some incidents with a notable number of trolling comments include: