Plain English Meaning

A turn where the circle you draw on the ground stays the same size all the way around, even though the wind is trying to blow you off course. To make that happen, you keep adjusting how steeply you bank the airplane as you go around.

Full Definition

A turn flown so that the airplane's flight path traces a circle of unchanging radius over the ground, regardless of wind. Because wind continually pushes the airplane during the turn, the pilot must vary the bank angle throughout — steepening it when the groundspeed is highest (downwind) and shallowing it when the groundspeed is lowest (upwind) — to keep the radius from the ground reference point constant.