sacrum

The sacrum is a large, triangular bone at the base of the spine. It is formed when five lower vertebrae fuse into one strong structure, usually by early adulthood. Resting between the two hip bones, it links the spine to the pelvis and helps hold the lower body together. You can think of it as a central support point: it carries weight from the upper body, helps keep the pelvis stable, and provides a strong base for standing, walking, and sitting.

In anatomy, the sacrum is also important because several nerves pass through or near this area on their way to the legs and pelvic organs. That is why doctors often mention it when talking about lower back pain, sacroiliac joint problems, fractures, or nerve-related symptoms. The word itself has an old history and is connected to the idea of a "sacred bone," which is why it can sound unusual outside medical contexts.

The word is most often used in medical, biological, and educational writing. In everyday language, most people simply think of it as the bone at the very bottom of the spine, just above the tailbone. So when you hear "sacrum," picture the broad triangular part that connects your back to your hips and helps support the body's frame.