Your spine is made up of a series of bones (vertebrae) that are stacked on top of each other from your tailbone (coccyx) to your skull, with soft cushions of gel-like tissue (discs) between them. There’s a hole in the middle of each vertebra and your spinal column runs through the opening, called the spinal canal. Nerves spread out from the spinal cord through spaces in the bone and travel to different points in your body.
Spinal stenosis is the narrowing of the space inside your backbone (spinal column). This can happen when either bone or something else presses on or constricts the spinal cord or nerve roots.
Image credit: Medical Gallery of Blausen Medical 2014(external link)