The definition of a bully is a person that picks on or beats smaller people.
Things that I have heard and seen that might be bullying is as following:
Someone beating up each other
(Vague area) cursing
Stealing from people
He can stand up for himself or he can tell a teacher
As a whole, there is really nothing I can do. Sure I can tell a teacher but people won't care at this school and still do it.