The term 'backbone segment' can be defined as a VERTEBRA, which is an individual bone in the spinal column. Vertebrae are stacked on top of each other to form the backbone, and they provide support for the body while also protecting the spinal cord. Each VERTEBRA has a unique shape and size, and they are connected to each other by ligaments and muscles. The vertebrae also allow for movement of the spine, and they are essential for maintaining posture.