Definition
A short-range radar system used by air traffic control to detect and display the position of aircraft within roughly 60 nautical miles of an airport. It provides azimuth and range information but not altitude, and is the primary radar used for sequencing and separating arriving and departing traffic in the terminal area.
Plain English
A radar at or near the airport that shows controllers where nearby aircraft are, so they can line them up safely for landing and takeoff. It tells the controller direction and distance, but not how high the aircraft is.
Context Anchor
You may see ASR in discussions of radar services, approach control, and radar approaches near airports.
Derivation
Airport Surveillance Radar — "surveillance" comes from the French sur- (over) and veiller (to watch), literally "watching over." The name reflects its job: continuously watching the airspace around an airport.
Why Pilots Care
Provides a backup means of navigation guidance and traffic separation when other aids are unavailable or weather prevents visual approaches.
Intuition Check
ASR is the radar system itself. An ASR approach is a specific use of that system, not a different meaning of the abbreviation.
Example Sentence 1
Approach offered us an ASR approach to Runway 27 after our GPS failed.
Example Sentence 2
During the ASR approach the pilot received altitude and heading instructions from the radar controller.