What portion of the spine is commonly called the tail bone?

The portion of the spine commonly referred to as the tailbone is the coccyx. This small, triangular bone is located at the very end of the vertebral column and consists of three to five fused vertebrae. The coccyx serves as an attachment site for ligaments and muscles, playing a role in supporting the pelvic organs and maintaining posture when sitting.

Understanding the coccyx's function and location is essential for anatomical knowledge, particularly in fields related to medicine and radiography. The other areas mentioned—the lumbar spine (which is located in the lower back), the thoracic spine (in the upper and mid-back), and the sacrum (which is situated above the coccyx and comprises fused vertebrae contributing to the pelvis)—do not refer directly to the tailbone. Each of these segments has distinct features and functions within the spinal column, but the coccyx is uniquely identified as the tailbone.