Plain English Meaning
A small indicator on the cockpit display that tells the pilot whether the airplane is on, above, or below the correct downward path to the runway during an approach.
Full Definition
A display element on an electronic flight display that shows the aircraft's vertical position relative to a desired descent path during an instrument approach. It typically appears as a moving pointer or diamond on a fixed vertical scale next to the attitude indicator, deflecting up when the aircraft is below the path and down when above. It receives signals from a precision approach aid (such as an ILS glideslope) or from a vertical guidance source generated by the (such as or ).