Overview
Back pain is common, and so is the confusing language that comes with it. This glossary collects the terms you'll see across InjuryAtlas's lower back pages and explains each one in plain English.
Terms are listed alphabetically. Each definition is short on purpose — follow the links for the full picture.
A
Annulus fibrosus: The tough outer ring of an intervertebral disc. It contains the softer centre and can develop tears, which is how discs begin to bulge or herniate.
Anterior: A direction term meaning toward the front of the body.
B
Bulging disc: A disc whose outer wall has stretched or pushed outward without breaking open. Bulges are common and many are painless — they are not the same as a herniated disc.
C
Cauda equina: The bundle of nerve roots at the bottom of the spinal cord, named for its horsetail appearance. Compression here is a surgical emergency — see back pain red flags.
Core: The muscles of the trunk — abdominals, back extensors, diaphragm, pelvic floor and gluteals — that work together to support and control the spine.
D
Dermatome: The area of skin supplied by a single nerve root. Patterns of numbness or tingling can help map where a nerve is irritated.
Disc (intervertebral disc): The shock-absorbing cushion between two spinal vertebrae. Each disc has a tough outer ring and a soft jelly-like centre. See intervertebral disc anatomy.
E
Erector spinae: The group of long muscles that run alongside the spine and straighten it. They are one of the main muscle groups behind the back. See erector spinae anatomy.
Extension: Bending backward, or straightening, of the spine.
F
Facet joints: The small paired joints at the back of each spinal level that guide and limit spine movement. They can become stiff, irritated or arthritic. See lumbar facet joint pain.
Flexion: Bending forward, or rounding, of the spine.
H
Herniated disc: A disc whose soft inner material has pushed through a tear in the outer ring, sometimes touching a nerve root. See lumbar disc herniation.
Hip hinge: A bending pattern where the hips move backward and the spine stays long, rather than rounding the lower back. It is a core skill for safe lifting.
I
Intervertebral disc: The cushion between vertebrae. See Disc.
L
Leg pain (sciatica): Pain, tingling or numbness that travels from the back down the leg. It usually means a nerve is irritated, not necessarily that the disc is "out." See leg pain and sciatica.
Lordosis: The natural inward curve of the lower back. A normal amount is healthy; the curve varies from person to person.
Lumbar spine: The five largest vertebrae in the lower back (L1–L5), which carry most of the body's weight. See lumbar spine overview.
Lumbar spinal stenosis: Narrowing of the spinal canal that can squeeze the nerves, often causing pain and heaviness in the legs with walking. See lumbar spinal stenosis.
M
Myotome: The group of muscles supplied by a single nerve root. Weakness patterns can help identify which nerve is involved.
N
Nerve root: The part of a spinal nerve that branches off the spinal cord between vertebrae and travels toward the body.
Neutral spine: A mid-range spine position that keeps the natural curves and is often the most comfortable and efficient position for lifting and loading.
Nucleus pulposus: The soft jelly-like centre of an intervertebral disc.
P
Piriformis: A small muscle deep in the buttock that helps rotate the hip. It sits close to the sciatic nerve, and irritation here can mimic sciatica. See piriformis syndrome.
Posture: The position of the body against gravity. Static "perfect posture" matters less than variety and the ability to move in and out of positions comfortably.
Psoas major: A deep hip-flexor muscle that connects the lumbar spine to the thigh. When tight, it can pull on the lower back. See psoas major anatomy.
Q
Quadratus lumborum: A deep muscle on each side of the lower back that stabilises the spine and pelvis and lifts the hip. See quadratus lumborum anatomy.
R
Radiculopathy: Nerve-root irritation that causes symptoms along the nerve's path — commonly pain, tingling, numbness or weakness in the leg.
Referred pain: Pain felt away from its true source. For example, a hip problem can feel like buttock or back pain.
Red flags: Warning signs that suggest something more serious and need prompt medical assessment — fever, loss of bowel or bladder control, saddle numbness, or severe progressive weakness. See back pain red flags.
Rotation: Twisting movement of the spine around its vertical axis.
S
Sacroiliac (SI) joint: The strong joint where the sacrum meets the pelvis on each side. It moves very little but can be a source of buttock and lower-back pain. See sacroiliac joint dysfunction.
Sciatic nerve: The largest nerve in the body, running from the lower spine through the buttock and down the back of the leg. See sciatic nerve anatomy.
Spasm: A sudden, involuntary contraction of a muscle. Back spasms are the muscle's protective response, not the injury itself.
Spondylolysis: A stress fracture or defect in the bony bridge at the back of a vertebra, common in younger athletes with repeated extension and rotation.
Spondylolisthesis: When a vertebra slips forward over the one below it, sometimes due to spondylolysis. See spondylolysis and spondylolisthesis.
Strain: A muscle or tendon injury from overload — a "pulled muscle." See low back strain.
T
Trigger point: A tight, tender spot within a muscle that can refer pain to other areas. Releasing it can help, but it is rarely the whole story in back pain.
Related Resources
This information is for education only and is not a medical diagnosis. If you have severe pain, loss of bowel or bladder control, numbness in the saddle area, or progressive leg weakness, seek medical care urgently.