Definition
A generic term covering the range of services provided to aircraft by air traffic control authorities, including flight information service, alerting service, air traffic advisory service, and air traffic control service (area, approach, and aerodrome control).
Plain English
ATS is the umbrella name for all the services that air traffic providers give to aircraft, from passing along flight information to actively controlling traffic.
Context Anchor
You may see ATS in FAA and international material when the text is talking broadly about services provided by air traffic facilities, not just one controller or one tower.
Why Pilots Care
Knowing the scope of available ATS determines what help a pilot can expect in different airspace classes and phases of flight.
Intuition Check
Do not read ATS as only air traffic control. Air traffic control is one part of ATS; ATS is the broader category of services that support aircraft operations.
Example Sentence 1
The flight crossed into a region where ATS was limited to flight information and alerting only, with no radar coverage.
Example Sentence 2
ATS provides both traffic advisories and full separation services depending on the airspace.