A serous membrane is a thin layer of tissue that lines certain cavities in the body and covers the organs within those cavities. It produces a fluid called serous fluid, which acts as a lubricant, reducing friction between the organs as they move. This membrane is essential for the proper functioning of organs in areas such as the thoracic cavity and abdominal cavity. There are two main layers of a serous membrane: the parietal layer, which lines the cavity wall, and the visceral layer, which covers the organs themselves. Examples of serous membranes include the pleura around the lungs, the pericardium surrounding the heart, and the peritoneum in the abdominal cavity.