What is a tetrapod?

A tetrapod is a vertebrate animal with four limbs. "Tetra" means "four" and "pod" means "foot".

Amphibians, reptiles, birds and mammals are all tetrapods; even snakes and other limbless reptiles and amphibians are tetrapods because they descended from animals which had four limbs. Whales and other cetaceans are also tetrapods because they are mammals have two front limbs and the two hind limbs are vestiges.