A generic term which has been used to refer to a number of means of mass transit. Various definitions include: a bus operation which operates within a major employment or residential area as the final leg of a commuter's journey and circulates constantly with bus and rail stops; a means of mass transit such as a moving sidewalk or a monorail used to transport people along a fixed route; a fully automated, grade-separated transit system serving a relatively small area such as an airport, downtown district, or theme park.