Empyema means the collection of pus within a body cavity but when you are talking about the pleural cavity it is another word, pyothorax. Pyothorax is the correct term to use when you are talking about the accumulation of pus in the pleural cavity.

The term pleurisy (pleuritis) is inflammation or infection in the pleural space around the lungs.

Pyothorax also known as empyema of the pleural cavity is the presence of pus in the pleural cavity between the layers of the pleural membrane Py/o - Pus