This document discusses empyema, which is the accumulation of pus in the pleural space. It describes the etiology as being infections like pneumonia or tuberculosis. The pathophysiology involves infection, inflammation, and increased capillary permeability that allows fluid containing white blood cells and proteins to accumulate in the pleural space. Over time, this can progress to adhesion and thickening of the pleural membranes. The document outlines the diagnostic process and management approaches like thoracentesis, pleurodesis to prevent further fluid buildup, and decortication to remove fibrous tissue.