A stud in animal breeding is a male animal, such as a horse or dog, that is employed for breeding. The terms for the male of a given animal species (stallion, bull, rooster, etc.) usually mean that the animal is entire, that is, not castrated, and therefore capable of standing at stud. A specialized vocabulary exists for de-sexed animals.
A stud farm, in animal husbandry, is an establishment for selective breeding using stud animals.