The coccyx is a triangular arrangement of bone that makes up the very bottom portion of the spine below the sacrum. It represents a vestigial tail, hence the common term tailbone. Depending on an individual’s development, the coccyx may consist of three to five different bones connected by fused—or semi-fused—joints and/or disc-like ligaments. The coccyx connects with the sacrum through the sacrococcygeal joint, and there is normally limited movement between the coccyx and the sacrum.

Source: Spine Health