Plain English Meaning
A VOR ground station that sits on the airport property. Because the station is right at the airport, flying to the station is the same as flying to the airport, so it can be used as the final point on the approach.
Full Definition
A VOR (VHF Omnidirectional Range) navigation transmitter located on the airport itself, which can serve as the final approach fix for a VOR instrument approach to that airport. When the VOR is on the airport, the approach is flown to the station rather than to a fix defined by a radial and distance from it.
Context Anchor
Seen on VOR instrument approach procedures when the navigation station used for the approach is located on the airport itself.