Plain English Meaning
An ATS Route is an officially published path through the sky that aircraft follow so air traffic controllers can manage traffic in an organized way. It is a general label that covers several specific kinds of routes, including low-altitude airways, high-altitude jet routes, GPS-based routes, and the standard paths used for arrivals and departures.
Full Definition
A specified route designed for channeling the flow of traffic as necessary for the provision of air traffic services. The term ATS Route is a generic term that includes Victor airways, jet routes, area navigation (RNAV) routes, and and routes. An ATS route is defined by route specifications which may include an ATS route designator, the path to or from significant points, distance between significant points, reporting requirements, and the lowest as determined by the appropriate authority.