Visual Glide Slope Indicator
Visual Glide Slope Indicator or Visual Glideslope Indicator (VGSI) is a ground device that uses lights to assist a pilot in landing an airplane at an airport. The lights define a vertical approach path during the final approach to a runway and can help the pilot determine if the airplane is too high or too low for an optimum landing.
Source: Wikipedia — Visual Glide Slope Indicator (CC BY-SA 4.0)