A stallion is an uncastrated male horse that is kept for breeding purposes. Stallions follow the conformation and phenotype of their breed, but within that standard, the presence of hormones such as testosterone can give stallions a unique appearance and behavior. The term "stallion" can also be used to refer to males of other equids, including zebras and donkeys.

Some key points about stallions include:

• Behavior: Stallions can exhibit aggressive behavior towards other horses and humans if not properly socialized or handled. Some stallions must be confined and cannot be kept in a natural setting due to their dangerous behavior. However, stallions can be trained to focus on work and can be brilliant performers if properly handled.

• Herd behavior: Stallions can be kept in a male-only group of stallions or with stallions and geldings. Some managers provide stallions daily turnout by themselves in a field where they can see, smell, and hear other horses.

• Appearance: Stallions follow the conformation and phenotype of their breed, but within that standard, the presence of hormones such as testosterone can give stallions a unique appearance.

Overall, stallions are primarily kept for breeding purposes.