Any of various aquatic or terrestrial reptiles of the order Testudines (or Chelonia), having horny toothless jaws and a bony or leathery shell into which the head, limbs, and tail can be withdrawn in most species.
Any of an order (Testudines syn. Chelonia) of terrestrial, freshwater, and marine reptiles that have a toothless horny beak and a shell of bony dermal plates usually covered with horny shields enclosing the trunk and into which the head, limbs, and tail usually may be withdrawn.