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.