The same as glide path. It provides vertical guidance for aircraft during approaches and landings. The glide slope, or glide path, is based on the following:

i. Electronic components emitting signals that provide vertical guidance by referring to airborne instruments, such as an ILS/MIS (instrument landing system/microwave landing system), during instrument approaches.

ii. Visual ground aids, such as VASI (visual approach slope indicator), which provide vertical guidance for a VFR (visual flight rules) approach or for the visual portion of an instrument approach and landing.

iii. PAR (precision approach radar), which is used by ATC (air traffic control) to inform an aircraft making a PAR approach of its vertical position (elevation) relative to the descent profile.