Family:  Within a breed, a strain with its own particular characteristics and line of descent (as the Denmarks, Chiefs, and Highlanders of the American Saddle Horse breed).

Feather:  Hair on the legs, particularly on the back of the cannons and fetlocks.

Fetlock (and fetlock joint):  The cushionlike projection, usually bearing a tuft of hair, on the back side of the leg above the hoof.  The fetlock joint is located between the great pastern bone (first phalanx) and the metacarpus or metatarsus.  Literally "foot-lock" (of hair) or "feet-lock."  The fetlock joint is sometimes erroneously called "ankle."

Field Master:  In hunting, charged with keeping the day's hunt running smoothly.  Unlike the huntsman, who rides in the lead with full attention on the fox and the pack, the field master looks after the riders in the field, sees that gates are not left open, notes any damage to property, etc.

Filly:  A young female horse, up to three years old (or whatever age is considered "adult," sometimes four or five).

Flat Racing:  Racing over short courses without jumps.  A test of speed at the gallop, originating in England, and almost exclusively confined to Thoroughbreds.  (I should add that this may no longer be true, as racing native breeds is becoming more and more popular and, as far as I know, racing with Arabs, Quarter Horses, etc., is still considered "flat racing.")

Foal:  A baby horse, male or female, up to one year old (or until it becomes a weanling).  Also, a mare "foals" when she gives birth.

Format:  Height at the withers in relation to length of the rump.

Foundation Sire (or Mare):  A stallion, or mare, whose progeny have been a major contribution in the formation of a breed.

Frog:  V-shaped elastic horn on the sole of the hoof acting as a shock absorber and extending back to the heel.