The word for a male horse is "stallion." Stallions are typically uncastrated male horses that have not undergone surgical procedures to remove their reproductive organs. They are known for their often stronger physiques and are usually used for breeding purposes. Stallions can exhibit more aggressive behavior compared to geldings (castrated male horses) and mares (female horses), which can affect their management and training. Thoroughbred racing and various equestrian disciplines often rely on stallions for their progeny and breeding programs.