A weanling is an animal that has just been weaned. The term is usually used to refer to a type of young horse, a foal that has been weaned, usually between six months and a year. Once it is a year old, the horse is referred to as a yearling. A weanling is an animal that has just been weaned. The term is usually used to refer to a type of young horse, a foal that has been weaned, usually between six months and a year. Once it is a year old, the horse is referred to as a yearling. The word is also sometimes used to describe young cattle and pigs, but 'weaner' is more common in the United States.