This is a common term and can also be described as a bulging disc, slipped disc or swollen disc.
They all basically mean the same thing. A disc is made up of a very tough, outer layer (annular fiber) with a liquid center (nucleus). When the interior fibers closest to the liquid start to tear or create fissure, the liquid will start to follow that path of least resistance toward the outside. At a certain point the remaining fibers will no longer be able to maintain the shape of the disc and therefore a swelling or herniation will occur. The swollen or herniated disc puts pressure on the nerve root coming off the spinal cord. This causes mild to severe pain. And that pain can cause a person not to be able to stand up straight or to stand in a leaned position to one side (antalgic lean). The medical treatment is an x-ray and/or MRI followed by medication (anti-inflammatory, pain killer, muscle relaxer). These are usually very ineffective and the person then ends up in physical therapy and finally surgery.
Chiropractic can treat a herniated disc more effectively and faster in most cases. By simply using an adjustment herniated disc can be relaxed. Sometimes treatment includes that adjustment combined with traction and possible spinal decompression. The person feels better, gets back to work faster, and has a stronger back with less chance of recurring.