A claw is a curved, pointed appendage, found at the end of a toe or finger in most amniotes (mammals and reptiles, including birds). However, the word "claw" is also often used in reference to an invertebrate. Somewhat similar fine hooked structures are found in arthropods such as beetles and spiders, at the end of the leg or tarsus for gripping a surface as the creature walks. Crabs', lobsters' and scorpions' pincers, or more formally, their "chelae", are sometimes called claws.
A claw is made of hard protein called keratin. Claws are used to catch and hold prey in carnivorous mammals such as cats and dogs, but may also be used for such purposes as digging, climbing trees, self-defense etc., in those and other species.
Similar appendages that are flat and do not come to a sharp point are called nails instead. Claw-like projections that do not form at the end of digits, but spring from other parts of the foot are properly named spurs.
Claws of animals like tigers, lions, and bears were used in making items such as ornaments, pendants, and brooches. Tigers' and lions' claws are expensive because it is illegal to trade the parts of such protected animals.