Polydactyly or polydactylism (from Ancient Greek πολύς (polus) "many" + δάκτυλος (daktulos) "finger"), also known as hyperdactyly, is a congenital physical anomaly

Congenital disorder

A congenital disorder, or congenital disease, is a condition existing at birth and often before birth, or that develops during the first month of life , regardless of causation...

 in human

Human

Humans are the only living species in the Homo genus...

s, dog

Dog

The domestic dog is a domesticated form of the gray wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The dog may have been the first animal to be domesticated, and has been the most widely kept working, hunting, and companion animal in...

s, and cat

Cat

The cat , also known as the domestic cat or housecat to distinguish it from other felids and felines, is a small, usually furry, domesticated, carnivorous mammal that is valued by humans for its companionship and for its ability to hunt vermin and household pests...

s having supernumerary

Supernumerary body part

Supernumerary body parts are most commonly a congenital disorder involving the growth of an additional part of the body and a deviation from the body plan. Body parts may be easily visible or hidden away, such as internal organs....

 fingers or toes.
The extra digit is usually a small piece of soft tissue that can be removed. Occasionally it contains bone without joints; rarely it may be a complete, functioning digit.