An aberration in behavior; in particular, an obsessive behavior of unconventional sexuality.
Abnormal behavior; that is, behavior that deviates from the norms or the laws of a society or group, and so invokes social sanctions, controls, or stigma.
Deviance is a relative concept: what is considered deviant in some societies may be normal in others; in a particular society the same act (killing someone, for example) may be either normal or deviant depending on the circumstances (in wartime or for money, for example). Some sociologists argue that the reaction of others, rather than the act itself, is what determines whether an act is deviant, and that deviance is merely behavior other people so label.