Bullying includes teasing and name-calling, spreading nasty rumours, abusive or threatening texts or emails, intimidation and violence.
There's often a fine line between some of this behaviour. What's considered gentle teasing by one child might appear as intimidation to another.
There's no doubt that for some children and young people, bullying - however defined - is the most stressful experience of their lives.
Some fear it so much they refuse to go to school or find excuses to avoid situations where bullying can occur. At the most extreme level, bullying can on rare occasions lead to a suicide attempt. This is why it must always be taken seriously.
Children have to accept a certain level of teasing, and parents need to provide support so the child can deal with this. However, physical threats or continual taunting is distressing and should never be tolerated.
Some children and young people are more likely to be the victims of bullying than others. Those with an obvious physical characteristic, such as being overweight, can become targets, as can those with some form of disability. Those who are shy or diffident, or who find it hard to stand up for themselves, may also be vulnerable.
Victims of bullying often feel ashamed of what's happening and blame themselves. It's here that friends and important adults have a key role to play. Bullying victims need support to see that it's not their fault and that something can be done to help them.
When bullying occurs, most of the attention is focused - not surprisingly - on the victim. But we need to pay attention to the bully, too. Not all bullies are the same; research has shown that there are differences between the ringleaders, the 'henchmen' and the silent observers, for example.
Bullies are often people who've been bullied themselves, and may be vulnerable and angry. A lot can be done to help them deal with their pain and avoid taking it out on others.
Most people assume that bullying happens exclusively at school. However, it can happen elsewhere too such as online and sometimes at home, possibly by an older sibling.
Adults can do an enormous amount to help, although sometimes it can be difficult to see how to proceed.
If your child is showing signs of stress and you aren't sure what's going on, bullying may be one possible cause.
All schools are required to have an anti-bullying strategy in place. As a parent, you can find out if this is working. If it isn't, get support from other parents to insist that it does.
If you do find that your child is being bullied offer help but be sensitive. Simply rushing to the school and demanding action isn't necessarily the best tactic.
Young people are often anxious about any move a parent might make, and may fear reprisals from the bullies if action is taken by the school.
The best thing to do is talk things over with your child and plan a strategy that suits them. This may involve getting support from friends or other parents, a quiet talk with a trusted teacher or even thinking about changing schools.
The most important thing is to offer support in a way that feels right for your child.