The Chiropractic Adjustment
An adjustment is a highly skilled and fast movement that is applied by the hand or in some instances an instrument to a joint in the body in order to loosen the joint. When this is done it is common to hear a "cracking" or "popping" noise. DO NOT worry, this is not your bones cracking or moving out of place. When the adjustment is applied it loosens the joint allowing a gas bubble to escape which creates the sound you may hear.
Mobilizations are similar to adjustments however they are much slower and you will not hear a "cracking" sound. Mobilizations are used to help decrease pain and increase joint mobility.