A limb (from the Old English lim) is a jointed, or prehensile (as octopus tentacles or new world monkey tails), appendage of the human or animal body; a large or main branch of a tree; a representative, branch or member of a group or organization.
Most animals use limbs for locomotion, such as walking, running, or climbing. Some animals can use their front limbs (or upper limbs in humans) to carry and manipulate objects. Some animals can also use hind limbs for manipulation.
In the human body, the upper and lower limbs are commonly called the arms and the legs. Human legs and feet are specialised for two-legged locomotion -- most other mammals walk and run on all four limbs. Human arms are weaker, but very mobile allowing us to reach at a wide range of distances and angles, and end in specialised hands capable of grasping and fine manipulation of objects.