Distance Measuring Equipment (DME)

Equipment (airborne and ground) used to measure, in nautical miles, the slant range distance of an aircraft from the DME navigational aid. (PCG definition).

A pulse-type electronic navigation system that shows the pilot, by an instrument-panel indication, the number of nautical miles between the aircraft and a ground station or waypoint.(PHAK definition)

Source: PCG, Pilot Handbook of Aeronatical Knowledge