An<unk>  () is a collection or gathering of pus within a naturally existing anatomical cavity. For example, pleural<unk>  is<unk>  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".
Empyema
Plastic bronchitis
Dust pneumonia
Emphysema
Bronchitis kettle
Atypical pneumonia
Lipid pneumonia
Pleurisy