What does "broke enough to rein" really mean?

Broke enough to rein means the horse has enough body control to perform advanced maneuvers without being forced into them through strong rein or leg pressure. The horse should steer softly left and right from a light rein, stop from a seat cue before the rein is needed, back willingly in a straight line, sidepass both directions, move its shoulders away from leg pressure, move its hindquarters away from leg pressure, collect its frame and extend it on cue, slow down from an extended lope to a collected one without pulling, and stay between the rider's reins and legs rather than leaning on one or the other. A horse that is only fast or only stops hard is not truly broke enough for reining — speed and stopping power without body control produces a horse that looks like a reining horse from a distance but cannot be shaped through the subtleties of a pattern correctly. The distinction matters because reining judges reward the quality and subtlety of the maneuvers, not just the execution of them. A horse that stops hard because it has been drilled into a hard stop but does not guide softly will show every gap in its foundation the moment the rider asks for a lead change, a spin, or a transition between circles. Broke enough to rein means the horse is broke all the way through — not broke enough to stop, not broke enough to spin, but broke in the full sense of the word: soft, responsive, balanced, and willing to move any part of its body in any direction from a light, specific cue delivered without force or anxiety.