WordNet
n. a farm where horses are bred
Wikipedia
A stud farm or stud in animal husbandry is an establishment for selective breeding of livestock. The word " stud" comes from the Old English stod meaning "herd of horses, place where horses are kept for breeding". Historically, documentation of the breedings that occur on a stud farm leads to the development of a stud book. Male animals made available for breeding to outside female animals are said to be "standing at stud", or at "stud service", referencing the relatively high probability that they are kept at a stud farm.
The word stud is often restricted to larger domesticated (especially farm) animals, such as cattle and horses. A specialized vocabulary exists for the studs of other animals, such as kennel (dog), cattery (cat) and aviary (birds).