The official birth date of all Thoroughbred racehorses is January 1 of the year they were born regardless of the actual birth date.
All horses are “foals” until they are a year old.
Between the ages of two and five, males are called colts while female horses are fillies.
Beyond the age of five, male horses are simply called horses while females are mares.
A male horse that has been neutered is referred to as a gelding while one preserved for breeding purposes is a stallion.
These designations are important because Thoroughbred racing uses age to determine equitable divisions for competition.
Gelding is from the Viking word geldr, which means “barren.”