Please define Drunk Driving for me

Found this article and was stuck in a quandry. Just the fact that things like this come up in our lives these days is crazy. Where do we get these ideas? It's over my head and smacked a bird. What's even crazier, is that I found it absurd right off the bat, just like when I heard that years old hashed up story of Kenny Chesney and Tim McGraw (aka the horse incident). It's a matter of using logic (which I'll fully admit doesn't work in most situations but totally applies here) I agree that the guys on horse back weren't drunk driving. They were drunk riding. Now if they were in a buggy, it'd be a whole different story. Then they would be driving. The point though is that automobiles are much more serious weapons in accidents.