Tripedalism
Tripedal (from the Latin tri = three + ped = foot) is the term used for (or would be used for) any animal that stands on three legs. The terms bipedal and quadrupedal are used more commonly when referring to animals that either walk on two legs (i.e. humans who walk upright) or animals such as dogs and cats who walk on four legs.
Read more about Tripedalism.