Empyema

An empyema (/ˌɛmpaɪˈiːmə/) is a collection or gathering of pus within a naturally existing anatomical cavity. The term is most commonly used to refer to pleural empyema, which is empyema of the pleural cavity. It must be differentiated from an abscess, which is a collection of pus in a newly formed cavity. The term is from Greek ἐμπύημα, "abscess".