The back is the posterior part of the human torso, extending from the base of the neck down to the lower waist or pelvis. It includes the spine (vertebral column), which provides structural support for the body and protects the spinal cord, a critical part of the nervous system. The spine is made up of individual vertebrae separated by intervertebral discs that cushion and allow flexibility.

Surrounding the spine are layers of muscles, tendons, and ligaments that aid in posture, movement, and stability. Key muscle groups include the trapezius, latissimus dorsi, and erector spinae, which facilitate movements such as bending, twisting, and lifting. The back also connects to the shoulders and hips, allowing coordination between the upper and lower body.

The skin and connective tissues covering the back provide protection and flexibility. Maintaining a healthy back is essential for mobility and overall well-being, as back pain or injury can significantly affect daily activities.