Which term describes the last three or four vertebrae of the spine, commonly referred to as the tailbone?

The term that describes the last three or four vertebrae of the spine, commonly referred to as the tailbone, is "coccyx." The coccyx is a small, triangular bone located at the very bottom of the vertebral column and is formed by the fusion of several vertebrae. It serves as an attachment site for various tendons, ligaments, and muscles, contributing to the stability of the pelvic region. Understanding the anatomy of the coccyx is crucial for recognizing its function in the overall structure of the spine, as well as its role in human biomechanics and posture.

In contrast, the sacrum refers to the five fused vertebrae forming the back part of the pelvis, while the lumbar and thoracic vertebrae consist of different segments in the lower and upper back, respectively. Each of these sections has distinct anatomical features and functions that do not correspond to the tailbone.