Delusional disorder refers to a psychotic disorder marked by severe delusions of grandeur, jealousy, persecution, or similar preoccupations; a psychotic disorder marked by a single striking psychotic symptom, an oraganized system of fixed, bizarre false belief , and persistent belief contrary to reality (delusion) but no other symptoms of schizophrenia, such as hallucinations, affective flattening, and additional symptoms of a thought disorder.
Other /More definition:
delusional disorder refers to a Psychotic disorder featuring a persistent belief contrary to reality (delusion) but no other symptoms of Schizophrenia.