Plain English Meaning
A 180-degree turn flown so the aircraft's path over the ground forms a perfect half-circle of the same width all the way around. Because wind keeps trying to push the airplane off that perfect arc, the pilot has to keep adjusting how steeply the wings are banked.
Full Definition
A half-circle turn flown so that the airplane's flight path traces an arc of unchanging radius over the ground, regardless of wind. To achieve this, the pilot must continuously vary the bank angle to compensate for the changing relationship between the airplane's heading and the wind direction during the turn.
Context Anchor
Used in ground reference maneuvers, especially S-turns across a road or other straight .