(1) delusions or prominent hallucinations (depending upon context, the person may or may not realize the hallucinations are not real). (2) Delusions, hallucinations, or other positive symptoms of Schizophrenia (i.e., disorganized speech, grossly disorganized or catatonic behavior). (3) A mental disorder which results in "impairment that grossly interferes with the capacity to meet ordinary demands of life" (outdated, from the DSM-II and ICD-9). (4) A loss of ego boundaries or a gross impairment in reality testing. [DSM-IV
this term causes confusion, because it is used in two different senses. In the past it was used to describe illnesses that are severe (e.g. dementia, schizophrenia and severe affective disorder). The other usage, which is more accepted nowadays, is referring to symptoms (hallucinations and delusions) that are qualitatively different to normal experience as opposed to quantitatively different (e.g. anxiety, depression).