Plain English Meaning

The direct, diagonal distance from your aircraft to a station on the ground — not the distance you would measure on a map. Since you are flying above the station, the straight line from you to it is longer than the distance across the ground.

Full Definition

The straight-line distance between an aircraft in flight and a ground-based station, measured along the line of sight rather than along the ground. Because the aircraft is above the station, this distance is always greater than the actual horizontal (ground) distance, with the difference becoming significant at high altitudes or when close to the station.

Context Anchor

Seen in DME error discussions, especially when the aircraft is high and close to the DME station.

Derivation

Slant comes from Middle English meaning to slope or lie at an angle. Range here means distance. Together: the distance measured along a sloping line — which is exactly what the signal travels between an aircraft above and a station below.