Definition
A ground-based navigation facility that combines a Non-Directional Beacon (NDB), which transmits a low/medium-frequency signal an aircraft's Automatic Direction Finder (ADF) can home to for bearing information, with Distance Measuring Equipment (DME), which provides the aircraft with slant-range distance to the station. Together they give the pilot both direction to and distance from a single fix.
Plain English
A ground station that does two jobs at once: it gives an aircraft a bearing toward it (the NDB part) and tells the aircraft how far away it is (the DME part).
Context Anchor
Seen on the top-down map portion of an instrument approach chart, where it may be used as a reference point or to show distances used during the procedure.
Derivation
Non-Directional means the beacon transmits equally in all directions, unlike a VOR which sends directional signals. Distance Measuring Equipment is named for exactly what it does. The slash combines the two co-located services into one charted facility.
Why Pilots Care
Provides both bearing and distance information for navigation fixes and certain non-precision approaches without requiring more advanced equipment.
Intuition Check
NDB/DME is not an either/or label. It means the chart is referring to a navigation aid with both NDB direction information and DME distance information available.
Example Sentence 1
The approach uses an NDB/DME on the field, so the pilot tracks inbound on the ADF and reads distance from the DME readout.
Example Sentence 2
On the approach plate the NDB/DME fix served as the initial approach waypoint.