Trolling is interacting with people, usually disingenuously, with the goal of eliciting a specific, usually negative, reaction. It certainly is possible to troll people by telling the truth (or without saying a word) and it’s certainly possible to be aiming for a reaction that isn’t negative, but usually there’s an element of being disingenuous to piss someone off.

Trolling is inevitable. Sometimes it’s politically motivated, sometimes it’s for fun, sometimes it’s literally a game with actual points. Some trolls are obvious, some are nearly impossible to tell from the genuine article.

The impact of trolling varies based on the subject, the target, and the method. Usually I find it’s best to ignore the possibility of trolling unless it’s obvious, simply due to the fact that assuming people are trolling may interfere with genuine communication, whereas assuming people are being genuine only interferes with meaningless interactions. Some say it’s better to ignore trolls, but personally I think it’s better to focus on content rather than intent. Interact when interaction is called for, ignore when it isn’t, and don’t pull your hair out wondering whether it’s a real conversation.