A biped is an animal that walks on two legs, with two feet. Human beings are one example of bipeds.
Most animals are not bipeds, but mammals that are include kangaroos and some primates. The ostrich, a giant, flightless bird, is the fastest living biped, and animals like bears and lizards are occasional bipeds. The word itself combines bi-, "twice or double" in Latin, and pedis, "foot." Four-footed animals, on the other hand, are quadrupeds.