A mare is an adult female horse or other equine.
Most of the time, a mare is a female horse over the age of three, and a filly is a female horse age three and younger. However, in Thoroughbred horse racing, a mare is defined as a female horse more than four years old; in harness racing a mare is a female horse more than three years old. The word can also be used for other female equine animals, particularly mules and zebras, though a female donkey is usually called a “jenny.” A broodmare is a mare used for breeding. A horse’s female parent is known as its dam.
An adult male horse is called a stallion, or, if castrated, a gelding. Occasionally the term “horse” is used in a restrictive sense to designate only a male horse.