Commonly known as DUI A criminal offense, operating a motor vehicle while under the influence of alcohol or drugs (including prescription.) Only impairment is required to the point where reflexes of the driver are materially impaired so that the driver may not be able to think clearly or drive safely. State laws specify the level of blood alcohol content (BAC) which constitute an offense and which the law presumes is a level at which a driver is detrimentally influenced. Also see driving while intoxicated or DWI in some states.