A grappling hook is a device that consists of a long rope with several metal claws at one end. Batman is one superhero who's famous for using a grappling hook to swing to safety while holding someone he has rescued.
Batman's grappling hook shoots out of a device he keeps on his belt, and it flawlessly wraps around and secures itself to any surface at which it's aimed. Real grappling hooks are less accurate, although they are real tools used by soldiers to board enemy ships and to dredge for objects submerged in water. This word comes from the verb grapple, "to seize hold of."