schizoaffective disorder is classified by the presence of delusions or hallucinations as well as symptoms of mood disorder.
From the Mayo Clinic:

The term "schizoaffective disorder" was introduced in 1933 by a doctor who determined that some patients showed symptoms different enough from schizophrenia to warrant a separate diagnosis. They experienced psychosis — such as hallucinations or delusions, characteristic of schizophrenia — and also had symptoms of elevated or depressed mood. Psychotic features and mood disturbances may occur at the same time or may appear on and off interchangeably. The course of the schizoaffective disorder usually features cycles of severe symptoms followed by an improved outlook. To establish a diagnosis, a person must have demonstrated, at some point, delusions or hallucinations for at least two weeks without evidence of mood disorder symptoms.