Definition
A device or system that transmits radio waves and listens for the reflections bouncing back from objects, using the time delay and direction of those returns to determine the range, bearing, and sometimes altitude of the object. In aviation, it is used by air traffic controllers to track aircraft and by airborne systems to detect weather, terrain, and other aircraft.
Plain English
A system that sends out radio signals, waits for them to bounce off something, and uses the bounce-back to figure out how far away that something is and which direction it lies in.
Context Anchor
Pilots encounter this term in discussions of radar services, weather radar, air traffic control surveillance, and equipment that detects nearby aircraft or terrain.
Derivation
The term is an acronym formed in the 1940s from Radio Detection And Ranging. "Detection" means finding the object; "ranging" means measuring how far away it is. The word RADAR has since become a standard English word in its own right.
Why Pilots Care
Radar is the backbone of how controllers see aircraft and provide separation, traffic advisories, and vectors. Pilots also rely on airborne weather radar to avoid thunderstorms and on ground-based radar services for safer flight in busy or low-visibility conditions.
Intuition Check
Do not read “radio” here as a voice radio call. In this term, radio waves are being used as a sensing tool: they go out, bounce back, and reveal where something is.
Example Sentence 1
The controller used radar to track the aircraft as it crossed the busy terminal area.
Example Sentence 2
Aircraft weather systems apply radio detection and ranging to show the location of precipitation ahead of the flight path.