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.

The anatomy of the human leg hints at the shared characteristics of tetropod legs (and to some extent wings and arms), and the requirements for leg anatomies in general.

The limb referred to in common parlance as the leg, is more accurately referred to, In the specific scientific terminology of human anatomy, as the "lower extremity" or "lower limb", Whereas in anatomical terms, the body part referred to as the "leg" is exclusively that portion of the lower extremity between the knee and the ankle (commonly known as the calf). The portion of the lower extremity above the knee is the thigh.

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In an extended sense, a leg is any part of an object that supports it off the ground. An example is the legs of a table or a chair.