The specific criminal offense may be called, depending on the jurisdiction, driving while intoxicated (DWI), operating while intoxicated (OWI), operating a motor vehicle while intoxicated (OMVI), driving under the influence [of alcohol or other drugs] (DUI), driving under the combined influence of alcohol and/or other drugs, driving under the influence per se or drunk in charge [of a vehicle]. Such laws usually (but not always) also apply to boating, piloting aircraft, or driving a bicycle.
Historically, guilt was established by observed driving symptoms, such as weaving; administering field sobriety tests, such as a walking a straight line heel-to-toe or standing on one leg for 30 seconds; and the arresting officer's subjective opinion of impairment. Limits for chemical tests are specific for blood alcohol concentration or concentration of alcohol in breath.
With the advent of a scientific test for blood alcohol content (BAC), enforcement regimes moved to pinning culpability for the offense to strict liability based on driving while having more than a prescribed amount of blood alcohol, although this does not preclude the simultaneous existence of the older subjective tests. BAC is most conveniently measured as a simple percent of alcohol in the blood by weight. It does not depend on any units of measurement.
What Does It Mean?
The validity of the testing equipment/methods and mathematical relationships for the measurement of breath and blood alcohol have been criticized. Driving while consuming alcohol may be illegal within a jurisdiction. In some it is illegal for an open container of an alcoholic beverage to be in the passenger compartment of a motor vehicle or in some specific area of that compartment.
Don't Be Your Own Worst Enemy
You should never talk to a police officer. However, if you simply cannot resist the urge, I suggest you say only the following: