Plain English Meaning

It means flying a curved path that stays the same distance from a ground station the whole way around. The pilot watches the distance readout and gently turns to keep that number steady, so the aircraft traces a portion of a circle around the station.

Full Definition

To navigate a curved flight path that maintains a constant distance from a navigation aid, where that distance is measured by Distance Measuring Equipment (DME) or, when permitted, by an equivalent GPS-derived distance. The pilot flies the arc by making small heading adjustments to keep the displayed distance from the station within a narrow tolerance, typically while transitioning from an enroute structure to a final approach course.