From AMS Glossary
A selectable interval of range (or of time delay from transmission) within which returning radar signals are measured.
Gating is used to isolate the echoes from different regions of distributed targets. Contiguous range gates of narrow width, separated by a distance equal to half the transmitted pulse length, are often used in lidar and weather radar systems. Some systems employ as many as a thousand range gates to measure the signals returned along each pointing direction.