Schizoaffective disorder is a disorder that is basically schizophrenia with also depression or manic episodes as well. So, schizophrenia, first of all, is a brain disorder that affects the development of the brain so that people's thinking and behavior are affected.
The main symptoms of schizophrenia include delusions, where people have fixed false beliefs about something, including feeling paranoid that other people are out to hurt them, or feeling grandiose like they have a mission to accomplish. These beliefs are not shared by other people in their culture.
There are hallucinations, where people may feel that they hear somebody talking to them and other people don't perceive that, or see things that other people don't see. There are disorganized thoughts and behavior, which affect how people are able to care for themselves and how they are able to communicate to others.
Then, there are negative symptoms where people may not have a lot of motivation to do things, and may have very flat affect, so that they do not seem like the people they were before they became ill. So, that's schizophrenia.
If you have schizophrenia and you also have periods of two weeks or more of depression, or you have periods of manic symptoms, where you have increased energy, talk too much, can't sleep, you have a lot of activity, then you might have schizoaffective disorder. What makes the schizophrenia plus mood episodes different than bipolar disorder, where you could have mood episodes and have delusions or hallucinations, the main difference is that in schizoaffective disorder, you have those delusions or hallucinations without depression or without that increased mood and increased energy that is associated with mania for some of the time. So, that schizophrenia is the primary diagnosis and then you have mood episodes on top of it.
So, that's sort of the long answer to what is schizoaffective disorder, which is still something that in psychiatry we're trying to learn more about. Sometimes people say, "I have schizophrenia and I have bipolar disorder." In that case, what they really mean, though, is that they have schizoaffective disorder, which captures the combination of both disorders.