Provides vertical guidance for aircraft during approach and landing. The glideslope/glidepath is based on the following:
  1. Electronic components emitting signals which provide vertical guidance by reference to airborne instruments during instrument approaches such as ILS; or,
  2. Visual ground aids, such as VASI, which provide vertical guidance for a VFR approach or for the visual portion of an instrument approach and landing.
  3. PAR. Used by ATC to inform an aircraft making a PAR approach of its vertical position (elevation) relative to the descent profile.

Source: Pilot Contoller Glossary (PCG)

See also: