A laminectomy is a procedure to remove the lamina, or the backmost parts of the vertebrae, to relieve pressure on the spinal canal and decompress the nerves. 

The surgeon makes incisions in the back over the vertebra, and moves the muscles away from the spinal cord. The lamina are then removed, exposing the nerves below and widening the central canal. Afterward, the facet joints may also be trimmed to relieve pressure on the nerve roots. A laminectomy is typically performed to treat spinal stenosis and may sometimes be used in conjunction with other procedures. 

Click here to see a lumbar laminectomy animation