The term of the lower back refers to three anatomical regions: the sacral, LUMBAR, and iliac regions. The sacral region is located at the base of the spine and is composed of five fused vertebrae. The LUMBAR region is located just above the sacral region and is composed of five separate vertebrae. The iliac region is located at the top of the spine and is composed of two bones that form the pelvis. All three regions are important for providing support and stability to the lower back.