Between 13 and 17 November, it is Anti-Bullying Week.
This is a special week to encourage everyone - children, teachers and parents - to take a stand against bullying throughout the year.
The theme this year is 'All different, all equal'. This is to highlight how everybody is unique and that we should celebrate the things that make us different from each other.
Here at Newsround, we have spoken to many of you about bullying.
But what exactly is bullying?
Bullying is when someone, or a group of people, repeatedly and intentionally hurt another person or people.
It can take different forms. For example, it could be physical (like pushing somebody around), emotional (for example, excluding someone) or verbal (such as calling somebody nasty names).
Bullies often do this to gain a sense of power over the person they are bullying, who is made to feel sad, scared or alone.
Bullying can happen in person face to face, or it can take place online - for example, via social media or games.
It often starts when people pick on something about someone that's different.
It could be about what they look like - for example, the colour of their skin - or who they are as a person - for example, how well they are doing at school or how good they are at something.
When bullying takes place online it is called cyberbullying. This form of bullying has become much more common, as many more young people have mobile phones and computers than they used to.
If you are worried that you or anyone that you know is being bullied, speak to an adult that you trust you about it. That might be a teacher or someone in your family.
Or you can call ChildLine for free on 0800 1111.