- a median septum or partition between two parts of an organ, or paired cavities of the body.
- the partition separating the right and left thoracic cavities, formed of the two inner pleural walls, and, in humans, comprising all the viscera of the thorax except the lungs.
- a membrane between two parts of an organ or cavity such as the pleural tissue between the two lungs
- the part of the thoracic cavity that lies between the lungs, containing the heart, trachea, etc
