Stalking happens when someone follows or bothers another person over and over again, even when the person who is being bothered tells them to stop or goes away from them.
Imagine if you were playing a game with your friend, and your friend didn't want to play anymore but you kept following them and asking to play again and again. That could be a little like stalking, because you're not respecting what your friend wants.
Stalking can make people feel really scared and upset. It's not okay to follow or bother someone when they don't want you to. If you or someone you know is being stalked, it's important to tell a grown-up you trust so they can help keep you safe.