The term "tail bone" refers to the last bone at the bottom of our spine, which is called the coccyx. It is a small bone that used to be longer, resembling a tail, in our ancestors. Full definition
Power jumps are good because, again, you land in a squat with tail bone extended. (hab-it.com)
All of this added up to a very sore tail bone and tight pelvic floor muscles and a lot of time to think about how travelling can affect your pelvic health. (bodyandbirthphysio.com)
Injuries from her time at Smyllum included a facial scar and broken tooth from being «slammed into a wall», broken fingers from being hit with a hair brush and a broken tail bone from having a seat pulled out from underneath her when she was sitting down. (premierchristianity.com)