A leg is a limb on an organism's body that supports the rest of the animal above the ground between the ankle and the hip and the groin. and is used for locomotion. The end of the leg farthest from the animal's body is often either modified or attached to another structure that is modified to disperse the animal's weight on the ground (see foot). In bipedal vertebrate animals, the two lower limbs are usually referred to as the "legs" and the two upper limbs as "arms" or "wings" as the case may be.

In the anatomy of vertebrates, including human beings (see human leg), leg is also used to refer to the entire limb, but its precise definition refers only to the segment between the knee and the ankle. In vertebrate and human anatomy this segment is also called the shank, and the front (anterior) of the segment is called the shin or pretibia.

Most animals have an even number of legs. Many taxonomic groups are characterized by the number of legs their members possess.