A claw is a sharp object. It is found at the end of a toe or finger in many mammals, birds, and some reptiles. The word "claw" is also used in reference to an invertebrate. For example, the chelae of crabs and lobsters are often called claws or pincers.
A claw is made of hard protein called keratin. They are used by some meat eating mammals such as cats to catch and hold prey, but they may also be used for other things such as digging, climbing trees, and so on, in those and other species.
Similar appendages that are flat and do not come to a sharp point are called nails instead.