empyema

thumb|Empyema

An empyema (; ) 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 is similar to or the same as abscess in meaning, but the context of use may sometimes be different. For instance, an appendicular empyema is in medicine now generally called an abscess.