Plain English Meaning
An ADF instrument where you can twist the numbered dial yourself so your heading lines up at the top. Once you do that, the needle points at the actual compass direction to the radio station.
Full Definition
An Automatic Direction Finder (ADF) indicator on which the compass card (the dial showing 0–360 degrees) can be rotated by hand using a knob, allowing the pilot to manually align the card so the aircraft's current magnetic heading sits at the top of the dial. Once aligned, the needle points to the magnetic bearing to the tuned non-directional beacon (NDB).