Plain English Meaning

An invisible sloped line in the sky, sent up from the runway, that tells the pilot whether they are descending at the right angle to land. Stay on it and the descent rate is correct; drift above or below and the aircraft is too high or too low.

Full Definition

The vertical guidance signal of an Instrument Landing System (ILS) or similar precision approach, transmitting an angled beam (typically 3 degrees) from a ground antenna near the touchdown zone that defines the correct descent path to the runway. '' is the term used with ILS; '' is the equivalent term used with () and certain other , but in everyday use the two words are treated as interchangeable.