An adjustment is often a pressure from the chiropractor utilizing the hands or an instrument to move a vertebrae back into place and/or restore proper movement of the vertebrae. You may hear a sound like the popping of your knuckles referred to as joint cavitation. It is the release of gases such as oxygen and nitrogen from the joint. 

Overall, adjustments are an excellent way to keep the body functioning at its highest level. When the body is in alignment, the body is able to respond and perform as it was designed to.