The condition of being born with 12 fingers (or extra fingers in general) is called polydactyly.
Polydactyly, also sometimes referred to as hyperdactyly, is a congenital condition where a person is born with more than the usual number of fingers or toes. It's one of the more common birth defects affecting the hands and feet. The extra digit can vary in size and form, ranging from a small nubbin to a fully formed, functional finger.
While the specific number of fingers isn't always twelve, polydactyly accurately describes the presence of extra digits. The condition can occur on one or both hands or feet.
