Answer : filly
A colt is indeed a male horse which is under the age of four. Whenever the colt reaches the age of four, anyone can describe him as the stallion, gelding, as well as just a horse.
Horses have been referred to in a variety of ways based on their age and gender. While colt solely refers to a little male, whereas filly refers to young female of the same age, one yearling is any horse of either sexes that is between one as well as two years of old. The term colt has been derived from Ancient English which originally signified “young ass” as well as “young camel.”