Foal In this context, a horse is considered a foal from the day its born until January 1 of the next calendar year, regardless of when in the year the foal was born.
Yearling A one year old horse
Juvenile A two year old horse
Filly A female horse that is younger than 5 years.
Colt A male horse that is younger than 5 years and not gelded
Mare A female horse that is 5 years or older
Stallion A non-gelded male horse
Horse A.) A member of the subspecies Equus ferus caballus.

 

B.) In a stricter sense within the thoroughbred industry, only a non-gelded male horse that is at least 5 years old is referred to as a horse.

Gelding A male horse that has been gelded (castrated)
Dam The mother of a horse
Sire The father of a horse
Broodmare A female horse used for breeding
Stud Male horse used for breeding
Broodmare Sire A sire whose female offspring has become producers of racehorses