The term 'spinal segment' refers to a section of the vertebral column, which is made up of 33 bones called vertebrae. The vertebrae are divided into five sections, and each section is referred to as a spinal segment. The four-letter answer to this crossword puzzle is DISC, which stands for intervertebral DISC. Intervertebral discs are located between the vertebrae and act as shock absorbers, allowing the spine to move freely and absorb impact.