Systematic harassing, pestering or attacking of a child by another child or group of children. More generally, it amounts to repeated oppression that can be psychological or physical of a less powerful person by a more powerful person, a definition that would include adult as well (e.g., workplace bullying). There are, however, a number of different definitions of bullying, but they seem to share three things in common: it consists of deliberately hurtful behavior (that would include malicious rumours or stories or exclusion from the social group), it occurs repeatedly over a period of time, and it is difficult for those being bullied to defend themselves.