1. A mental and behavioral disorder causing gross distortion or the disorganization of a person's mental capacity, affective response, and capacity to recognize reality, communicate, and relate to others to the degree of interfering with the person's capacity to cope with the ordinary demands of everyday life.

• Those associated with organic brain syndromes; such as, Korsakoff's syndrome.
• Those less strictly organic and having some functional component(s); for example, the schizophrenias, and bipolar disorders.

2. Generic term for any of the so-called insanities, the most common forms being the schizophrenias: "Melvin's doctor determined that he had a psychosis that consisted of a mental disorder in which he has a loss of contact with reality as well as personality disintegrations or the disorganizations of his psychic and behavioral mental processes."
3. A severe emotional and behavioral disorder: "The doctor told Derek's wife that her husband had a psychosis that includes a loss of reality contact, unlike a neurotic disorder in which reality contact is retained."