filly
Breeding: Female horse four-years-old or younger.
Harness racing: A female horse 3 years of age or younger.
foal(ed)
1) A horse of either sex in its first year of life. 2) As a verb, to give birth. Also known as “dropped.” 3) Can also denote the offspring of either a male or female parent.
founding sires
The Darley Arabian, Byerly Turk and Godolphin Barb. Every Thoroughbred must be able to trace its parentage to one of the three founding sires.
full-brother, full-sister
Horses that share the same sire and dam.