In zoological anatomy, a leg is any one of the parts of an animal's body that (in most legged species and at most times) separate the rest of the body from the ground, and are used for locomotion.
Legs are most common in one of the even-numbered quantities of 2 or 4 (in vertebrates), or 6, 8, or 12 (in arthropods); the legs of centipedes and millipedes are much more numerous (but seldom exactly a hundred or a thousand as their names might suggest).
A two-legged animal is a biped.
A four-legged animal is a quadruped.
Anatomy of human leg