empyema

An empyema is a collection or gathering of pus within a naturally existing anatomical cavity. For example, pleural empyema 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'.

the pleural cavity (pleural empyema also known as pyothorax)

the uterus (pyometra)

the appendix (appendicitis)

the meninges (subdural empyema)

the joints (septic arthritis)