A vertebra is one of the small bones that stack up on top of each other to form your backbone. Each one has a hole in the middle, and when they are stacked the holes line up into a tunnel that protects the spinal cord — the thick bundle of nerves running from your brain down your back. Between the bones sit soft pads (discs) that let you bend and twist; a 'slipped disc' is one of those pads pushing out where it should not. Humans have about thirty-three of them, though the bottom ones fuse together in adults. The tricky part is the plural: one vertebra, but two or more vertebrae. That plural is Latin and is usually said 'VER-tuh-bray' or 'VER-tuh-bree' — both are heard. You will see this word in health talk, sports injuries and biology class. In relaxed conversation people just say 'a bone in my back'; if you say 'I cracked a vertebra', you sound precise and slightly medical, which is often exactly what you want at a clinic.