Insanity, craziness or madness is a spectrum of behaviors characterized by certain abnormal mental or behavioral patterns. Insanity may manifest as violations of societal norms
Norm (sociology)
Social norms are the accepted behaviors within a society or group. This sociological and social psychological term has been defined as "the rules that a group uses for appropriate and inappropriate values, beliefs, attitudes and behaviors. These rules may be explicit or implicit...

, including becoming a danger to themselves and others, though not all such acts are considered insanity. In modern usage insanity is most commonly encountered as an informal unscientific term denoting mental instability, or in the narrow legal context of the insanity defense.

The definition of insanity is doing the same thing over and over again and expecting a different result.

Transactions of the … North American Wildlife and Natural Resources Conference, Volume 71 (Wildlife Management Institute, 1975), p. 54 (attributed to Albert Einstein).

Insanity is doing the same thing, over and over again, but expecting different results.

Rita Mae Brown, Sudden Death (Bantam Books, New York, 1983), p. 68 (attributed to Jane Fulton).