A mutt is a dog whose parents were different breeds, or whose ancestry includes many different breeds mixed together. While some dogs are purebreds (meaning their parents, grandparents, and great-grandparents were all the same breed, like golden retrievers or beagles), a mutt might have a cocker spaniel parent and a terrier parent, or an even more complicated family tree going back generations.

The word is informal and can be affectionate. Dog lovers sometimes prefer mutts because they may be healthier than some purebreds, combining traits from different breeds. A mutt might have the intelligence of a border collie mixed with the friendliness of a Labrador. Some people call them mixed-breed dogs in formal settings, but many dog owners happily call their beloved pets mutts.

Sometimes people jokingly call themselves mutts when talking about their own diverse ancestry. Used this way, it can be a warm way of celebrating having roots in many different places.