Traditionally, insanity or madness is the behaviour whereby a person flouts societal norms and becomes a danger to himself and others. Greek tragedies and Shakespeare often refer to madness in this sense. Psychologically, it's a general popular and legal term defining behaviour influenced by mental instability. It is defined by the Merriam-Webster dictionary as a deranged state of the mind or lack of understanding. Today, it's most commonly encountered as an informal term or in the narrow legal… (More on Insanity)