Coccyx/ˈkɑːksɪks/ Definition 1 of 1Pro Tip 1/3Location Specificity The coccyx is specifically at the very base of the spine, not elsewhere. My lower back hurts, but it's not my coccyx; it's higher up. Pro Tip 2/3Injury Reference Coccyx is often mentioned in the context of injuries or discomfort. After slipping on ice, I ended up with a sore coccyx. Pro Tip 3/3Evolutionary Relic The coccyx is a vestigial structure, once a tail in ancestors. Humans have a coccyx, indicating our evolutionary past.