Plain English Meaning
The arrow on the ADF gauge that always points toward the radio station the receiver is tuned to. Whichever way the arrow points, that is the direction of the station from the aircraft.
Full Definition
The pointer on an Automatic Direction Finder (ADF) instrument that rotates to indicate the direction of a tuned non-directional radio beacon (NDB) relative to the aircraft. On a fixed-card ADF, the needle points to the relative bearing from the nose; on a movable-card or Radio Magnetic Indicator (RMI), the needle points to the magnetic bearing to the station.