Plain English Meaning
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.
Full 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.
Context Anchor
Seen on cockpit navigation displays during an Instrument Landing System approach, usually as a vertical guidance indication beside or within the main display.