Aeronautical mobile service (short: AMS; also: aeronautical mobile radiocommunication service') is a form of aviation communication conducted through radio. The ITU Radio Regulations divide AMS into communication used for civil air route flights (R) and off-route flights (OR). Aeronautical mobile (R) service is a so-called safety-of-life service, must be protected for interferences, and is an essential part of air traffic control. Communication occurs between radio stations onboard aircraft, termed aircraft stations, and terrestrial stations that are sometimes termed "aeronautical stations". Communication can also occur between aircraft.[1] AMS is commonly used in air traffic control.