back

The back is the posterior region of the human torso, extending from the base of the skull to the pelvis. It contains the spine, spinal cord, nerves, muscles, and connective tissues, and it supports the body's weight in an upright posture while enabling a wide range of movements.

The spine, or vertebral column, is made up of 24 movable vertebrae divided into the cervical, thoracic, and lumbar regions, plus the sacrum and coccyx. Intervertebral discs cushion the joints between vertebrae. The spinal cord runs within the vertebral canal, with pairs of spinal nerves exiting between the vertebrae. Back muscles include the large superficial muscles such as the trapezius and latissimus dorsi, and deeper layers like the erector spinae and multifidus, which stabilize and move the spine. Ligaments and fascia also help support the back.

Functionally, the back provides structural support for the body, enables bending, lifting, and twisting, and protects the spinal cord and nerve roots. Common health concerns involve the back region; low back pain is a frequent condition with a range of causes, including muscle strain, herniated discs, degenerative changes, and arthritis. Management typically involves a combination of rest, physical therapy, exercise, pain medications, and, in some cases, injections or surgery. Prevention focuses on maintaining good posture, core strength, flexibility, and ergonomic practices.

In addition to anatomy, the term back has other uses. It can denote the rear side of an object or the opposite of front, or function as a verb meaning to support someone or something, or to move in reverse. The word appears in many phrases and contexts beyond the body.