RADAR is an acronym for Radio Detection and Ranging. It is a radiolocation system that uses radio waves to determine the distance, angle, and radial velocity of objects relative to the site. The term RADAR was coined in 1940 by the United States Navy. The system was developed secretly for military use by several countries in the period before and during World War II. The modern uses of radar are highly diverse, including air and terrestrial traffic control, radar astronomy, air-defense systems, anti-missile systems, marine radars to locate landmarks and other ships, aircraft anti-collision systems, ocean surveillance systems, outer space surveillance and rendezvous systems, meteorological precipitation monitoring, altimetry and flight control systems, guided missile target locating systems, self-driving cars, and ground-penetrating radar for geological observation.