The following terms are used to describe the gender of a horse or pony at different ages.

Filly - A female horse or pony under 4 years of age.

Colt - A male horse or pony under 4 years of age that has not been gelded (castrated).

Foal - A female or male horse or pony under 1 year of age. A female foal is known as a "Filly Foal", a male foal is known as a "Colt Foal". Foals that have been weaned can also be called "Weanlings".

Yearling - A female or male horse that is between 1 and 2 years old. A female yearling is known as a "Yearling Filly", an male yearling that has not been gelded (castrated) is known as a "Yearling Colt".

Mare - A female horse or pony that is 4 years or older.

Stallion - A male horse or pony that is 4 years or older that has not been gelded (castrated). Stallions are also known as "Entire".

Gelding - A male horse or pony of any age that has been gelded (castrated).

Rig - A male horse or pony who has either one or both testes undescended and retained or a male horse that has been improperly castrated. Rigs can display stallion tendencies, especially around mares.