A partition or a dividing wall between two spaces or cavities: "The septum is a medical term for a thin separation within, or between, certain parts of the body; for example, the nasal septum is the sheet of cartilage and bone that separates the nostrils of the nose."

A sheet of connective tissue that separates the two halves of the togue.

A thin plate of brain tissue, containing nerve cells and fibers, that is stretched like a flat, vertical sheet between the column and body of fornix (arched bundle of fibers); a triangular double membrane situated in the median plane and separating the anterior horns of the lateral ventricles of the brain.