An uncastrated male horse younger than 4 years is referred to as?

A young uncastrated male horse under the age of 4 is called a colt. This term specifically designates male horses before they reach maturity, which typically occurs when they are around 3 to 4 years old.

In contrast, the other terms refer to different categories of horses. A filly is a young female horse, while a stallion refers to an adult male horse that is also uncastrated but older than 4 years. Additionally, a gelding is a male horse that has been castrated, making it incapable of reproduction. Therefore, the distinction of age and reproductive status is crucial when identifying the terms used in equine terminology, and "colt" specifically describes the young male horse in this context.