Definitions for "Mediastinum"
A partition; a septum; specifically, the folds of the pleura (and the space included between them) which divide the thorax into a right and left cavity. The space included between these folds of the pleura, called the mediastinal space, contains the heart and gives passage to the esophagus and great blood vessels.
a broad, median partition, actually a mass of tissue found between the pleurae of the lungs; it extends from the sternum to the vertebral column
the compartment in the chest region that houses the heart and organs located between the lobes of the lung.