Answer: So you are wondering what a male horse is called? Male horses are called different words, depending on their age and other factors.
A male horse, when it is born, is called a colt.
Most colts are gelded (the horse term for neutering) between the ages of 6 months and 18 months. A male colt that is ungelded is called a "stud colt".
After the age of two years male horses are correctly referred to as geldings ("neutered") or stallions (un"neutered").
A stallion can also be referred to as a "stud".