Instrument landing system
From AMS Glossary
instrument landing system
(Abbreviated ILS.) A navigational aid used to facilitate the landing of an aircraft in instrument weather at an airport.
The instrument landing system consists of two parts: 1) a directional guide to bring the plane to the correct runway; and 2) a glide path to bring the plane down at the correct glide angle or slope to touch the runway at the correct point. Current safety requirements demand that visual contact with the ground be possible within the final several hundred feet of descent.