Plain English Meaning
If your destination airport doesn't have its own current altimeter setting, you use the setting from a nearby reporting station that the FAA has designated for that purpose.
Full Definition
An authorized altimeter setting from a weather reporting station located away from the airport of intended operation, used when the airport itself does not have a local altimeter source available. The remote source is specified by the FAA for that airport and is applied with any required altitude adjustments published on the approach procedure.
Context Anchor
Seen on instrument approach charts and in altimeter setting when the destination airport does not provide a .