Through socialization and social control, society ensures the maintenance of social system. Majority of the people adhere to the social norms of the society. But we cannot say that all the members in the society will stick to the norms of the society.
Thus, deviant behavior is any behavior that fail to conform to some specified standard. Deviant behavior disturbs the social equilibrium. It is contravention of the social norms. It is a departure from the usual modes of behaviour.