The legal definitions of "driving" and "drunk" are open to many interpretations, which vary greatly from state to state. In some places, "driving" can include sitting still in a parked or wrecked vehicle with the motor off, or starting up a car in a driveway. Police can and do arrest people whom they believe are drunk before they get on the road and even when they've pulled off to "sleep it off," just if they're in the driver's seat. As for the definition of "drunk," there are several major factors to consider. You can be "legally impaired" as viewed by the law without ever taking a drink, if you have taken other substances like prescription drugs that affect your ability to drive. You can also be found drunk even when you can function properly in every way.
You can be found guilty of drunk driving, also called driving while intoxicated (DWI) or driving under the influence (DUI), if the state can prove that you have more then the legal limit of alcohol in your system. Even if your alcohol level is lower than the legal intoxication level, you can still be convicted if the state can show your abilities were impaired.
Blood tests