Distortion and overdrive, although similar in the idea, refer to 2 levels of gain. Overdrive is a smoother subtle gain usually generated by tubes or anolog overdrive pedals...this provides that crunch type infamous sound. Distortion is usually associated with heavy gain, for metal etc, and can easly be provided by digital pedals and amps. Although saying that overdrive and distortion is common to one type of equipment is a bit of a misstatement.