n.1. a bundle or group of nerve fibers within the central nervous system. The name of a tract typically indicates its site of origin followed by its site of termination; for example, the reticulospinal tract runs from the reticular formation of the brainstem to the spinal cord. Compare nerve. 2. a series of organs that as a whole accomplishes a specific function (e.g., the digestive tract). 3. a region, passage, or pathway.