Trolls post messages on public interactive forums. They will often, not always, post anonymously or use a false name.
Realistically there are two definitions of “trolling”. Both are important and in both instances the behaviour described is unkind and unacceptable.
The first definition describes a troll as anyone who, typically for their own twisted amusement, uses an interactive online forum deliberately to post messages intended to provoke or upset someone or a group of people. The perpetrator might try to convince themselves and their friends it’s just a joke, but to victims it is anything but, particularly if what is going on becomes known all around school.
Alternatively, trolling is where someone, either alone or as part of a group, again in a public forum, intentionally attacks an individual in an unusually horrible, threatening, aggressive or highly personal way.
Attacks on prominent people because of the colour of their skin, country of origin or religion, their sexuality or political beliefs, or on a person who has bravely spoken out on a subject, is the kind of trolling with which we are sadly very familiar. Many women in public life have suffered in that way. In some instances, this has caused them to step down and it has discouraged other women from coming forward.
In all cases the answer is the same. If a post makes you feel uncomfortable, do not respond. Do not engage. It will only encourage a troll to carry on. Tell your parents or teacher, block the person posting and report it to the platform concerned. If you are really worried about a threat of violence or theft, the police should be informed.
Some trolls are part of highly organized groups with a political or social agenda which they hope to advance by trolling. They believe it will help them find and recruit new people to their cause.
With the first type of trolling, the perpetrator may well be known to the victim but that just makes it worse, not better. If you think it’s someone at school, perhaps a teacher or other responsible adult could mediate to stop repeat attacks but, as stated, the perpetrator should always be blocked straight away if the message is upsetting.
Trolling is different from cyber stalking or harassment because they usually happen via direct messaging, one on one, although the intentions are often the same: to hurt, upset or provoke.