An acronym for radio detection and ranging, the original and basic function of radar. The name is applied to both the technique and the equipment used. Radar is a sensor; its purpose is to provide estimates of certain characteristics of its surroundings of interest to a user, commonly the presence, position, and motion of aircraft, ships, or other vehicles in its vicinity. In other uses, radars provide information about the Earth's surface (or that of other astronomical bodies) or about meteorological conditions. To provide the user with a full range of sensor capability, radars are often used in combinations or with other elements of the complete system.