Peritonitis is an inflammation of the peritoneum, typically caused by infections from bacteria or fungi, leading to severe abdominal pain and other symptoms such as fever and vomiting. There are two types: primary spontaneous and secondary peritonitis, both of which can be life-threatening due to various causes like liver disease or ruptured organs. Diagnosis involves various examinations and imaging techniques, and treatment includes antibiotics, surgery, and preventive measures to reduce infection risk.