Radar
Definition
Finding things with radio echoes — from air-traffic control to your car's blind-spot warning.
Technical definition
RAdio Detection And Ranging: transmit pulses, then measure echo delay (range) and Doppler shift (speed). Range resolution is ~c/2B.
Example
Police speed guns are Doppler radar — the frequency shift of the reflected microwaves reads your speed directly.
Common confusion
Radar doesn't produce a photograph — it plots echoes by distance and direction. Reading the blips correctly is a skill in itself.