Definition
The vertical guidance component of an Instrument Landing System (ILS) that transmits a narrow radio beam angled upward from near the runway touchdown zone, typically at about 3 degrees, allowing a properly equipped aircraft to follow a precise descent path to the runway during an instrument approach.
Plain English
It's the radio beam an aircraft follows down to the runway that tells the pilot whether they are too high, too low, or right on the correct descent angle for landing.
Context Anchor
Seen during instrument approach training, approach briefings, and cockpit instrument indications when flying an ILS approach.
Derivation
Glide' refers to the steady descent of the aircraft, and 'slope' refers to the angle of that descent. Together they describe the sloped path the aircraft glides down to reach the runway.
Why Pilots Care
It supplies the vertical path needed for a stabilized descent and safe touchdown when visibility is too low for visual landing.
Intuition Check
Do not think of the glideslope as the runway itself or as a visual line painted outside. It is electronic vertical guidance shown to the pilot by the aircraft instruments.
Example Sentence 1
Cleared for the ILS approach, the pilot intercepted the glideslope at 2,000 feet and began a steady descent to the runway.
Example Sentence 2
Passing the final approach fix, the aircraft was slightly high on the ILS glideslope.