Epilepsy is a common condition and it can affect anybody, at any age.
It usually starts in childhood, or in people over 60, and more than half a million people in the UK have been diagnosed with it.
It affects a person's brain and causes frequent seizures.
According to the charity Epilepsy Action, around one in every 240 children under the age of 16 in the UK will be diagnosed with epilepsy.
"Epilepsy is when something unusual happens in your brain. Your brain is like a very powerful computer. It controls everything you do. When your brain starts sending too many electrical messages, this can make different things happen to your body. These things have lots of names, like fits, seizures, funny turns and attacks."
Doctors don't always know why someone has epilepsy.
It might be because they've suffered a serious head injury or had a bad infection when they were a baby.
Another reason can be if it's a condition other family members have.
It's not something that can be caught from someone else.
If someone has epilepsy, they usually have it throughout their life, but in some cases it can improve over time.
It can be difficult and sometimes dangerous, because it's not always possible to know when someone is going to have a seizure.
Most people are able to live normal lives if their seizures are well controlled.
Children can take part in most activities and sports, but people might have to think about how their condition could affect things such as driving, swimming and certain jobs.
Charity Epilepsy Society has advice for young people living with the condition.
"If you do feel down or worried about your epilepsy, you're not alone. Many young people with epilepsy may have the same worries that you have. Some people find that talking about their concerns can help. There are lots of ways that you can connect with other people and get support.
"It doesn't matter who you decide to talk to, as long as you feel you can trust them and that they are good at listening. It could be a friend, a family member or your GP."
There are lots of different types of seizures - at least 40 - and they can affect people in different ways.
It can be hard for people to describe exactly how it feels because they might not even be aware that they're having a seizure until it's all over.
Seizures can include getting a funny taste in their mouth, going stiff, then falling to the floor and jerking.
Most don't last long - a few minutes or a few seconds - but they can happen suddenly. This can be dangerous depending on what someone is doing at the time or where they are.
It is rare, but sometimes a person with epilepsy can die during or after a seizure for no obvious reason. This is known as sudden unexpected death in epilepsy - or SUDEP.
There are loads of people living with epilepsy who don't let their condition affect them or hold them back. The most important thing is to talk to friends and family about it, get on with your life, go out and keep active.
For some people, medicine or an operation on their brain can stop seizures.
Following a very special diet can also help, and some children grow out of their epilepsy.
Purple day is on 26 March and happens every year.
People all over the world use the day to raise awareness of the condition and raise money for charities which support people with epilepsy.
The idea came from a young girl in Canada called Cassidy Megan who has epilepsy and wanted others with it to know they're not alone. She wanted more people to talk about the condition.
The colour purple was chosen because lavender is the international flower of epilepsy.
If you have any more questions about the condition or want to find out more, speak to an adult that you trust - maybe a parent, teacher or another relative - or you can speak to your local doctor, who will have lots of information and advice if you need.