Deviance is defined by sociologists as any behavior that violates significant social norms.
All societies have norms. These are values or other ideas about what is and is not right. Some of these norms are made into laws and people who break them are punished by the legal system. Other norms remain simply as social conventions. People who break them are not punished by law but are stigmatized by society.
Deviance, then, can take many forms. Stealing cars is a form of deviance. But so is something like using profane language in public settings, which is not illegal. Deviance is any behavior that violates important norms of the society in which it occurs.