Ostracism was a method of: 1. punishing criminals
2. preventing politicians from gaining too much power.
3. rewarding excellence.
4. determining the guilt of the accused.​

1) Punishing Criminals
This method of punishment was not only used for criminals, but primarily with people who were viewed as enemies of the state.
This came most prominently from Ancient Greece as the people gathered once a year to ostracize/banish one person from Athens. This person was selected and voted on because they were seen as a “threat to democracy”. Anyone voted to be ostracized had to stay out of Athens for 10 years.
Today, this term is used frequently for anyone who is publicly shunned or looked down upon by society.