Bullying is when one child regularly harasses another child. This could be verbal bullying like name-calling, teasing, and using threatening language. It can also be physical abuse like punching, shoving, hitting, and spitting. It can be electronic too, via texting and the Internet. There is a gray area, however, that is important for parents to understand. If your child is regularly left out, by all means talk with the teacher.
Source: Great Kids!