Definition
A service provided by air traffic control radar facilities in which controllers, workload permitting, advise pilots of observed radar targets that may be in proximity to their aircraft. Information given includes the position of the traffic relative to the pilot's aircraft (using clock position), distance, direction of movement, and altitude if known. Also commonly called traffic advisories.
Plain English
It is a service where a radar controller tells you about other aircraft showing up on radar near you, so you can look for them and avoid getting too close.
Context Anchor
You may encounter this term when asking air traffic control for traffic advisories, especially during visual flight when you want help spotting nearby aircraft.
Derivation
Radar comes from the phrase radio detection and ranging. That helps because the service is based on detecting aircraft by radio-based surveillance and showing their position and distance on a controller’s display.
Why Pilots Care
Gives pilots early notice of other traffic so they can avoid mid-air conflicts and maintain safe separation.
Intuition Check
Do not assume “service” means the controller is keeping every aircraft separated from you. Here, it means the controller gives helpful traffic information when able, while the pilot still remains responsible for avoiding other aircraft.
Example Sentence 1
While receiving flight following, the controller passed traffic information: "Cessna Three-Four-Alpha, traffic eleven o'clock, three miles, eastbound, altitude indicates one thousand five hundred."
Example Sentence 2
While on flight following, I received Radar Traffic Information Service for a helicopter crossing our path.