Scent:  In hunting, the smell of the fox, by which it is trailed by the pack.

School master:  Old, well-behaved, well-schooled horse or pony.  Safe and reliable for people learning to ride.

Selection:  Choice of the best horse for breeding purposes.

Shoulder in:  In dressage, the horse trots along wall of ring with head and shoulders curved toward center of ring and haunches parallel to wall.  Inside legs cross over in front of outside legs.

Show horse/pony:  Competes at shows in various classes, like "Working Hunter" or "Children's Riding Pony."  Judged on its appearance, schooling and suitability for the class entered.

Show jumping:  Jumping competitions.

Shy, Spook:  The way a horse deals with objects or sounds that frighten him.  Shying is ducking sideways suddenly.  Spooking is stopping, suddenly, then reacting.  It is difficult and unpleasant to ride a spooky horse.

Sire:  A stallion, the father of a foal.  Also, the verb for the same sense, as in "to sire a foal" or "the foal was sired by..."  A sire's sire is a grandsire and so on.

Snaffle:  A mild bit that is broken in the middle.  The fatter the snaffle, the milder its action.

Spavin:  Bone enlargement of the hock, causing lameness.

Splay-footed:  Stance with toes of forelegs wide apart.

Stallion:  An ungelded (unneutered) adult male horse, more than three years old.  Usually difficult to handle and kept only for breeding.  Sometimes called an entire or a stud.

Steeplechase, steeplechasing:  Race run over fences on courses which are about five miles long.  Racing over obstacles.

Stern:  In hunting, the tail of a hound.

Stifle (or stifle joint):  The joint next above the hock, and near the flank, in the hind leg, corresponding to the knee in man.  The word is of uncertain origin.  The stifle bone is the patella, or kneecap.

Stocking:  A color term used to describe a leg that is white up to the knee (in front) or the hock (in back).  See The Exterior diagram.

Stud:  A stallion used for breeding; also, a breeding farm.

Stud book:  The record book of a breed, naming sire and dam of each horse registered.

Suckling:  A young horse of either sex; more commonly called a foal.

Sulky:  Light two-wheeled vehicle used in harness racing.