Is it Bullying?

We've all been there: your child comes home from school upset because a classmate was unkind to them. Perhaps this has happened before and maybe now you're wondering how best to handle it? It's always good to let your child's teacher know so that he or she can help but when is it considered "bullying"?
Bullying is defined as any aggressive and unwanted behavior that is intended to harm, intimidate, or humiliate the victim; involves a real or perceived power imbalance between aggressor or aggressors and victim; and is repeated over time or causes severe emotional trauma. Bullying includes cyber bullying. Bullying does not include ordinary teasing, horseplay, argument, or peer conflict.