The tiny area between the two layers of the pleura (the thin covering that protects and cushions the lungs). The pleural space is normally filled with a small amount of fluid. See the entire definition of Pleural space
Space (10 µm) between parietal and visceral pleura in chest; contains pleural fluid acting as lubricant which enables the lungs to slide against the chest wall. Pressure is negative and changes with the respiratory cycle. See intrapleural pressure, respiratory pump.