Plain English Meaning
A way for the aircraft to know where it is by measuring how far it is from two ground-based distance stations, with an onboard motion-sensing system filling in whenever those distance signals are weak or unavailable.
Full Definition
A method of area navigation (RNAV) position determination in which the aircraft computes its position by measuring distances from two or more DME ground stations, supplemented by an Inertial Reference Unit (IRU) that maintains position information using onboard motion sensors. The IRU bridges gaps in DME coverage and improves position accuracy when fewer than two suitable DME stations are available.
Context Anchor
Seen in RNAV departure and instrument procedure discussions when describing what navigation sources an aircraft may use to meet the required path accuracy.