A mongrel, mutt, or mixed-breed dog is any dog which does not belong to one officially recognized breed. While such terms may refer to all dogs of mixed breeds, the terms "dog crossbreed" and "designer dog" specifically refer to mixed-breed dogs which are intentionally bred.
Mixed-breed dogs may have ancestries that include any combination of purebred dogs and other mongrels.
A dog breed is a particular type of dog that was purposefully bred by humans to perform specific tasks, such as herding, hunting, and guarding. Dogs are the most variable mammal on Earth, with artificial selection producing upward of 360 globally recognized breeds. These breeds possess distinct traits related to morphology, which include body size and shape, tail phenotype, fur type, etc., but are only one species of dog. Their behavioral traits include guarding, herding, and hunting, and personality traits such as hyper-social behavior, boldness, and aggression. Most breeds were derived from small numbers of founders within the last 200 years. As a result of their adaptability to many environments and breedability for human needs, today dogs are the most abundant carnivore species and are dispersed around the world.
A dog breed will consistently produce the physical traits, movement and temperament that were developed over decades of selective breeding. For each breed they recognize, kennel clubs and breed registries usually maintain and publish a breed standard which is a written description of the ideal specimen of the breed. Other uses of the term breed when referring to dogs include pure breeds, cross-breeds, mixed breeds and natural breeds.