The coccyx, also known as the tailbone, is a small, triangular bone resembling a shortened tail located at the bottom of the spine. It is composed of three to five coccygeal vertebrae or spinal bones. The vertebrae may be fused together to form a single bone; however, in some cases, the first vertebra is separate from the others.

The coccyx is connected to the sacrum by means of an amphiarthrodial joint. This is a type of joint that functionally only allows for a slight amount of movement. Later in life, the coccyx may fuse with the sacrum, though this is more common in women than in men. The coccyx serves as an attachment site for tendons, ligaments, and muscles. It also functions as an insertion point of some of the muscles of the pelvic floor. The coccyx also functions to support and stabilize a person while he or she is in a sitting position.

The coccyx may be fractured when a person falls abruptly on his or her buttocks. A woman's coccyx may be broken during a complicated childbirth. A qualified medical professional may prescribe pain medication until the coccyx heals. In extreme cases, the coccyx may need to be surgically removed. This procedure is called a coccygectomy.