Plain English Meaning
A simple radio beacon on the ground that sends a signal out in every direction. The aircraft's needle points toward it, so the pilot can tell which direction the station is. A Compass Locator is just a small version of this beacon, placed near a runway to help line up for an instrument approach.
Full Definition
A ground-based, low or medium frequency radio transmitter that broadcasts a signal in all directions, allowing an aircraft equipped with an Automatic Direction Finder (ADF) to determine bearing to or from the station. A Compass Locator is a low-power NDB (typically 25 or less, with a of about 15 NM) installed at the outer or of an () to assist pilots in intercepting and the during an instrument approach.