Literally the word bully means bully a person who annoys weak people. How to disturb him, among others, by mocking, spreading rumors / instigating, isolating, intimidating (intimidating), threatening, oppressing, bullying, or physically abusing (pushing, slapping, hitting).
Based on this definition, bullying occurs because:

There is an imbalance of power between the bullying perpetrator and the target (victim). this power imbalance can be in the form of body size, physical strength, cleverness of speech or clever tongue, gender (sex), social status, feelings of superiority, etc.

Bullying can occur in any environment where social interaction occurs between humans, including;
School (School bullying) and campus. Workplace (Workplace bullying) and the community (thugs, motorbikes). Online (Cyberbullying), Political Environment (Political bullying), Military Environment (Military bullying), and in hazing.

Negative Effects of Bullying
In the long run, victims of bullying can suffer from emotional and behavioral problems. Bullying can cause feelings of insecurity, isolation, feelings of low self-esteem, depression or suffering from stress that can end in suicide.

Prevention Strategy
In several developed countries, including Australia, the United Kingdom, Canada and the United States, the problem of bullying has received the attention of their respective governments by making laws or regulations. In addition, anti-bullying program policies are held in every school and university.