A vertebrate is an animal that has a backbone — a spine made of small linked bones. Fish, frogs, snakes, birds and every mammal, including you, are vertebrates. Animals without one, like insects, worms, jellyfish and octopuses, are invertebrates, and they are actually the huge majority: vertebrates are a small minority of all animal species, even though they are the big, familiar animals we notice. The word works both as a noun ('a vertebrate') and as an adjective ('vertebrate animals', 'the vertebrate eye'). It belongs to biology class, nature documentaries and science writing; you would not use it over dinner unless you were talking about animals on purpose. One useful thing to know: having a backbone is only the headline feature. Biologists group vertebrates together because they share a whole package — a skull around the brain, an internal skeleton that grows with the body, and a nerve cord running along the back. That internal skeleton is why vertebrates can get large: a beetle's outside shell cannot be scaled up, but a bone frame can.