The vertebrae making up the portion of the spinal column that runs through the lower back.
The lumbar vertebrae are found below the thoracic vertebrae, which attach to ribs, and above the sacral vertebrae, which form the back of the pelvis. Unlike their neighbors, the lumbar vertebrae don't touch any other bones except the vertebrae themselves. This allows for considerable freedom of movement in the lumbar region, particularly in forward-backward motions (flexion and extension).
There are 5 lumbar vertebrae in the human skeleton, denoted L1 through L5, from top to bottom. The're bigger and more rugged than the vertabrae above; they have to be to support more of the body's weight.
In contrast to the cervical vertebrae, whose rearward spines slope sharply downward, the lumbar spines are close to perpendicular to their respective vertebral bodies and don't overlap one another. This makes the lumbar region more easily accessible for a spinal tap; indeed, the procedure is commonly called a lumbar puncture.
The great stress on the lumbar vertebrae makes them susceptible to degenerative diseases and sometimes misalignment, which can result in a herniated disc (a.k.a. slipped disc) or pinched nerve.