LIDAR is short for Light Detection And Ranging. It’s a more modern (but still pretty old) version of the tried and true radar which is short for Radio Detection And Ranging. Radar uses radio waves to detect objects and determine their range, angle, and/or velocity while lidar does basically the same thing, but with pulsed laser light rather than radio waves. Essentially, it is two different technologies that achieve the same goals.
LIDAR sensors find objects by emitting high-frequency laser light pulses and then measuring the time (in nanoseconds) it takes for some of those pulses to strike on the object, bounce back and strike the sensor. As the object moves, a processor inside the LIDAR sensor saves information about each returned pulse and can generate an accurate 3D image of the object, where it is relative to your equipment, which direction it is moving in, and how fast it is going. It is capable of creating highly detailed images, recreating details of less than an inch on an object that is more than 100 yards away. The downside is that it is an expensive technology as compared to RADAR.
If LIDAR is the pretty pony in the pasture, RADAR is the workhorse. Invented in 1940, RADAR does not return as accurate an object image as LIDAR, but it can do it in the rain, snow, sleet, hail, fog, mud, and dust. It is also more accurate than LIDAR at night and in cloudy conditions. RADAR works similarly to LIDAR, but it emits radio waves instead of laser beams.