The spine is made up of cervical, thoracic, and lumbar vertebrae. Below the lowest lumbar vertebra is the sacrum. The sacrum is a triangular shaped bone. After that comes the coccygeal vertebrae or coccyx.
The coccyx is the end of the spinal column. It's also triangle-shaped. This may be what could be referred to as a "tail." In fact, it is called the "tailbone."
The coccygeal vertebrae are fused together for the most part. In some people the first and second coccygeal segments may not be fused together. Several muscles and ligaments attach to the coccyx, but these don't allow us to move or wiggle the tailbone.