Complex sentence: Walkers have been constructed with anywhere from one to over eight legs; common configurations are one leg Pogo stick (hopper), two legs (biped), four legs (quadruped) and six legs (hexapod).
Split into simpler sentences: Walkers have been constructed with anywhere from one to more than eight legs. They are classified according to the number of legs with common configurations being one leg (pogo stick or "hopper"), two legs (biped), four legs (quadruped) and six legs (hexapod).