Jellyfish refers to a type of invertebrate marine animal that belongs to the phylum Cnidaria. They are characterized by their bell-shaped body, which is often transparent and contains stinging cells called cnidocytes. Jellyfish have been around for millions of years and can be found in oceans all over the world. Some species are known to migrate long distances across the ocean. They feed on small fish or zooplankton, using their tentacles to capture prey. While some jellyfish stings can cause discomfort, they generally do not pose a serious threat to humans unless there is an allergic reaction.