Vertebrate is any animal with a backbone. That bony or cartilaginous column running down the middle of your back? That makes you a vertebrate, along with dogs, cats, birds, fish, frogs, snakes, and whales.

The backbone is made of many small bones called vertebrae stacked on top of each other like building blocks. This design is clever because it's both strong and flexible. Your backbone protects your spinal cord (the main bundle of nerves connecting your brain to your body) while still letting you bend, twist, and move.

Vertebrates share other features too: most have a skull protecting their brain, and all have an internal skeleton rather than wearing their skeleton on the outside like insects do. Scientists divide vertebrates into five main groups: fish, amphibians (like frogs), reptiles, birds, and mammals. These groups look incredibly different from each other, yet they all share that fundamental backbone design.

The opposite of a vertebrate is an invertebrate, an animal without a backbone. Invertebrates include insects, spiders, worms, jellyfish, and octopuses. Interestingly, invertebrates make up about 97% of all animal species on Earth, but vertebrates tend to be larger and include the animals people find most familiar.