Plain English Meaning
A radio navigation station on the ground that tells pilots two things at once: which direction they are from the station, and how far away they are. It serves both civilian and military aircraft from the same site.
Full Definition
A ground-based navigation facility that combines a VOR (Very High Frequency Omnidirectional Range) and a TACAN (Tactical Air Navigation) station at the same site, sharing a single location and identifier. It provides civil aircraft with VOR azimuth (bearing) information and DME (Distance Measuring Equipment) range information from the TACAN component, while also providing military aircraft with full TACAN azimuth and range. Civil pilots use the VOR portion for direction and the DME portion of the TACAN for distance.