The coccyx (Latin: os coccygis) (pronounced kok-siks), commonly referred to as the tailbone, is the final segment of the human vertebral column, of four fused vertebrae (the coccygeal vertebrae) below the sacrum. It is attached to the sacrum in a fibrocartilaginous joint, which permits limited movement between them. The term coccyx comes originally from the Greek language and means "cuckoo," referring to the shape of a cuckoo's beak.