A leg is a weight-bearing and locomotive anatomical structure, usually having a columnar shape. During locomotion, legs function as "extensible struts". The combination of movements at all joints can be modeled as a single, linear element capable of changing length and rotating about an omnidirectional "hip" joint.
As a component of furniture, it is used for the economy of materials needed to provide the support for the useful surface such as the table top or chair seat.
Many taxa are characterized by the number of legs:
A leg is a structure of gross anatomy, meaning that it is large enough to be seen unaided. The components depend on the animal. In humans and other mammals, a leg includes the bones, muscles, tendons, ligaments, blood vessels, nerves, and skin. In insects, the leg includes most of these things, except that insects have an exoskeleton that replaces the function of both the bones and the skin.
Sometimes the end of the leg, or foot, is considered part of the leg; other times it is considered separate. Similarly, the hip joint or other place where the leg attaches to the main body may be considered separate or part of the leg.
In tetrapod anatomy, leg is used to refer to the entire limb. In human medicine the precise definition refers only to the segment between the knee and the ankle. This lower segment is also called the shank, and the front (anterior) of the segment is called the shin or pretibia.
A robotic leg is moved by an actuator, which is a type of motor for moving or controlling a mechanism or system. It is operated by a source of energy, usually in the form of an electric current, hydraulic fluid pressure or pneumatic pressure, and converts that energy into some kind of motion.
A prosthetic leg, a prosthesis, is an artificial leg that is used to replace one that has been lost.