The sacrum is a triangular bone located at the base of the spine, forming the back part of the pelvis. It consists of five fused vertebrae and connects the lumbar spine to the coccyx, or tailbone. The sacrum plays a crucial role in supporting the weight of the upper body when sitting and standing. In addition to its structural function, the sacrum is also important for the pelvic girdle, which includes the ilium, ischium, and pubis. It provides attachment points for various muscles and ligaments, contributing to the stability and movement of the lower body.