I sent a nasty message to someone in my class / my year. Am I a bully?
Would you say what you sent to them to their face? What would happen if you did? – would you end up in trouble? Saying horrible things about people isn’t pleasant and it often makes the person receiving them feel pretty rubbish. If you send these kinds of messages every day, or several times a day then you are making someone else’s life miserable and this is bullying. It doesn’t matter if you bully someone face to face or online, it’s still bullying.
You might end up in trouble if you regularly send nasty messages to the same person. Sometimes the police will even get involved.