A melee/thrown weapon and fishery tool consists of a metal rod with a sharp hooked blade at the end. Originally designed to impale fish or any marine creatures (whales, sharks, etc.) and bring up the catch after it was hooked by the blade.
There are several variants of harpoons, ranging from classic stabbing/throw variant, to larger version tied to a boat or ship to prevent the catch from escaping. Modern harpoon typically comes in to form of a harpoon gun to hit any potential catch with greater accuracy.