Adjustments, or manipulation as they're sometimes referred to is the minor movement of vertebrae in the spine. The objective of this movement is to realign vertebrae that have moved out of place for a number of reasons ranging from normal daily activity to trauma such as a car accident.
An adjustment is often a pressure from the chiropractor utilizing the hands or an instrument to move a vertebrae back into place. This happens with a quick movement and is often without discomfort. You may hear a noise that sounds like you're cracking 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.