Definition
An indicator on the ILS display that shows the aircraft's vertical position relative to the glideslope, the electronic descent path projected from the runway. When the pointer is centered, the aircraft is on the glideslope. When it deflects upward, the aircraft is below the glideslope; when it deflects downward, the aircraft is above the glideslope.
Plain English
A needle on the instrument panel that tells you whether you are on, above, or below the correct descent path to the runway during an instrument approach.
Context Anchor
Seen on cockpit navigation displays during an Instrument Landing System approach, usually as a vertical guidance indication beside or within the main course display.
Derivation
Glideslope' combines 'glide' (a steady descent) with 'slope' (an angled path). 'Pointer' is the moving needle that indicates a value. Together: the needle that shows where you sit on the descent path.
Why Pilots Care
Keeps the aircraft on the correct vertical path for a safe landing on the runway.
Intuition Check
Do not think of the pointer as the airplane itself. The pointer shows where the desired glide path is relative to you, so a high pointer means the path is above you and you are low.
Example Sentence 1
As we intercepted the glideslope, the glideslope pointer started moving down from the top of the display, and I began the descent.
Example Sentence 2
When the glideslope pointer rose above center, the airplane was below the desired descent path.