
Turning a horse by touching the reins to the side of the horse's neck. The horse turns away from the rein pressure. Particularly useful when riding one-handed. Compare bearing rein.
Found on
http://en.wikipedia.org/wiki/Glossary_of_equestrian_terms

A neck rein is a type of indirect rein aid. The horse responds to a neck rein when it has learned that a light pressure of the right rein against its neck on that side means for the horse to turn left, and vice versa. The neck rein is used in both English riding and in Western riding, though the style differs between the disciplines. In both disci...
Found on
http://en.wikipedia.org/wiki/Neck_rein

Movement of the rein against the horse's neck cues him to turn Also called a "brace rein" or "bearing rein"
Found on
http://www.gaitedhorses.net/Articles/HorseGlossary.html

A method of guiding the horse by placing the rein against its neck, moving the horse in the opposite direction. Both reins are held in one hand.
Found on
https://www.encyclo.co.uk/local/21481

to guide or direct (a horse) with the pressure of a rein on the opposite side of the neck from the direction in which the rider wishes to travel.
Found on
https://www.infoplease.com/dictionary/neck-rein
No exact match found.