Plain English Meaning
A radio signal at the runway that tells the pilot whether they are descending at the right angle to land. The cockpit display shows a needle the pilot keeps centered to stay on the correct slope down to the runway.
Full Definition
The vertical guidance signal provided by the glideslope component of an Instrument Landing System (ILS), giving pilots a precise descent path to the runway during an instrument approach. The glideslope transmitter, located near the touchdown zone, projects a narrow radio beam upward at a fixed angle (typically 3 degrees) that the 's ILS interprets and displays on the cockpit instruments, showing whether the aircraft is on, above, or below the correct descent path.