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.
The terms triped, tripedal and tripedalism are rarely, if ever, used in a real scientific context, as there are no known naturally occurring three-legged animals on Earth, although the movement of some Macropods such as kangaroos, which can alternate between resting their weight on their muscular tails and their two hind legs, may be an example of tripedal locomotion in animals. There are also the tripod fish. This fish rests on the ocean bottom on two rays from its two pelvic fins and one ray from its caudal fin .
Read more about Tripedalism: Quadrupedal Amputees and Mutations, Use of Tripedalism in Science Fiction and Fantasy, Mythological Tripedals