Schizophrenia is a severe brain disorder that causes difficulties distinguishing reality from fantasy, impaired thinking, emotional expression, social behavior, and normal functioning. It typically develops in late teens to early adulthood. Genetics and environmental factors both contribute to its development. Symptoms include positive symptoms like hallucinations and delusions, negative symptoms like lack of emotion, and cognitive symptoms like poor executive functioning. There is no medical test for diagnosis, which is based on psychiatric evaluation and presence of characteristic symptoms for a minimum duration.