What term describes the five-digit limb structure common to tetrapods?

The five-digit limb structure common to tetrapods is called the pentadactyl limb. “Penta-” means five, and “-dactyl” refers to digits, so the term describes the basic five-digit anatomical pattern seen in the limbs of many vertebrates.

Tetrapods are four-limbed vertebrates and include amphibians, reptiles, birds, and mammals. Their shared limb plan includes bones corresponding to the humerus, radius, ulna, wrist bones, and digits. The bones may be reshaped for very different jobs: a human arm grasps, a bat wing flies, and a whale flipper swims.

The pattern is an evolutionary homology, meaning the underlying arrangement was inherited from a common ancestor even when its outward form differs. Not every living tetrapod visibly has five digits. Horses have one main toe, birds commonly have three functional digits, and snakes have lost limbs entirely. Those modifications are evolutionary changes to the ancestral limb plan, not evidence that the shared pattern never existed.