A nail is a horn-like envelope covering the dorsal aspect of the terminal phalanges of fingers and toes in humans, most non-human primates, and a few other mammals. Nails are similar to claws, which are found on numerous other animals. Fingernails and toenails are made of a tough protein called keratin, as are animals' hooves and horns. The mammalian nail, claw, and hoof are all examples of unguis [plural ungues].
A horse hoof is a structure surrounding the distal phalanx of the 3rd digit (digit III of the basic pentadactyl limb of vertebrates, evolved into a single weight-bearing digit in equids) of each of the four limbs of Equus species, which is covered by complex soft tissue and keratinised (cornified) structures. Since a single digit must bear the full proportion of the animal's weight that is borne by that limb, the hoof is of vital importance to the horse. The phrase "no hoof, no horse" underlines how much the health and the strength of the hoof is crucial for horse soundness.