Plain English Meaning
The path you want to fly straight toward a ground radio station. If you stay on this path, you will arrive at the station.
Full Definition
In ADF (Automatic Direction Finder) navigation, the desired magnetic course the aircraft flies along to reach an NDB (non-directional beacon) station. The aircraft is on the correct inbound track when its heading and bearing to the station align with the planned course toward the beacon.
Context Anchor
Seen in ADF and traditional navigation procedures when a pilot is flying toward a ground radio beacon or toward a .