The serous membrane investing the lungs and lining the thoracic cavity, completely enclosing a potential space known as the pleural cavity. There are two pleurae, right and left, entirely distinct from each other. The pleura is moistened with a serous secretion that facilitates the movements of the lungs in the chest.

A double-folded membrane that covers each lung: The outer layer of the pleura, closest to the ribs, is the parietal pleura, while the inner layer, which is close to the lung, is the visceral pleura.

A thin, watery fluid, called the serous secretion keeps the pleura from being dry and facilitates the movements of the lungs within the chest or thorax.