Online bullying is when children or teenagers use the internet, phones or any other technology to threaten, tease or embarrass another young person.
It can happen in a number of different ways.
One example is sending nasty messages via phone, email or even on sites which have chat functions available.
Bullies could also set up a website or group and then ask other people to join in and comment about a person or pictures of them.
Other things that they might do include emailing someone a virus on purpose, posting personal information where it shouldn't be or calling someone names when playing a game together online.
Bullies on the web can't cause physical pain, but because of the way we now live our lives - with mobile phones and lots of internet use - they can be very hard to avoid.
Sometimes it is also difficult to know exactly who they are as they can hide behind fake names or pictures.
The most important thing that you can do to deal with online bullying - if you are worried that you or anybody you know is being affected - is to speak to an adult that you trust about it.
That might be a teacher at school or a member of your family.
They can help to advise you about the next steps to take if you have any concerns.
One of the best things to do to avoid online bullies is to avoid the spaces where they are being nasty.
That might be a website or it may mean blocking email addresses or mobile numbers that send nasty messages.
Many platforms have the option to report it if someone is being abusive or unkind, so you should report their behaviour to whoever is in charge of the platform.
Changing your username may also help and you should never give out personal details - such as your mobile number, address or email - online.
Protect your password too to keep your files and information safe.
It it also a good idea to keep evidence if anyone is being a bully online, so make sure that you keep any messages to pass them on to an adult that you trust.
If you are worried about online bullying, you can also call ChildLine for free on 0800 1111.