A thin layer of tissue covering the lungs and the wall of the chest cavity to protect and cushion the lungs A small amount of fluid that acts as a lubricant allows the lungs to move smoothly in the chest cavity during breathing SOURCE : http: //cancernet nci nih gov/dictionary html
double membrane lining the lung, the layer of tissue lining the inside of the chest wall is called the parietal pleura and the outside of the lung the visceral pleura