The coccyx bone is the tailbone, located at the very end of the spine. It is a vestige from an earlier evolutionary period.
Although the coccyx seems useless, it actually has a lot of influence over back pain (or lack of it) and events affecting the spine, such as childbirth. There are muscles and ligaments that attach to the coccyx, including pelvic floor structures. Being able to move the coccyx bone can relieve some forms of back pain. The movement of the coccyx bone is very subtle.