Schizophrenia is a severe disorder characterized by disorganized thinking, disturbed perceptions like hallucinations, and inappropriate emotions or actions. Symptoms include delusions, disorganized speech, lack of expression, and inappropriate behaviors like laughing at the wrong times. It typically develops in early adulthood and affects about 1 in 100 people, striking men more often than women. The causes are likely biological and related to abnormal brain development, though environmental factors during pregnancy like infection or malnutrition may also play a role.