Psychosis is one of the major symptoms of schizoaffective disorder; alongside mania/hypomania and depression.
The symptoms of psychosis consist of two different elements: hallucinations and delusional thinking.
Hallucinations are observations that no one else can observe. These can be auditory, visual, tactile, gustatory or olfactory in nature, and thus can affect all five senses.
Delusional thinking, meanwhile, is an absolute certainty in a thought or an idea that even evidence to the contrary does not shake.
The psychosis component of illnesses such as schizoaffective disorder are treated with antipsychotic medication (also known as major tranquilizers or neuroleptics) to reduce these symptoms.