Question: What is the difference between bipolar disorder and schizophrenia or schizoaffective disorder?
Answer: These distinctions are often more important in the textbooks than they are in reality.
But basically a bipolar disorder -- a bipolar person will have, between episodes of mania, periods of time when they are completely normal, when their mood is reasonable, when they are back to baseline. Also, both schizophrenia and schizoaffective disorder, by definition, include elements of psychosis, which bipolar disorder doesn't have to have. With schizophrenia -- the thought disorder -- or the psychosis, is present all the time. In schizoaffective disorder, the person essentially has the thought disorder all the time, with mood episodes superimposed upon it.
So you can have a situation in which a person is psychotic and not depressed or manic, but then is manic along with psychotic. So you can think of the psychosis as running in the background all the time in schizoaffective disorder with these mood episodes happening intermittently as well. Again the final piece of that would be in the bipolar disorder. Technically, the psychosis should only be present when the person is either manic or depressed. Not when they're euthymic or having a normal mood in between episodes.