What is an AVA and how does it affect the wine you drink?

I get this question more often than any other from readers and friends: just what the heck is an AVA anyway?
Take a breath while I get on my high horse here. The term takes a little explaining, and I’ve got some complaining to do while I’m at it. Some people think it’s associated with quality. Not necessarily.
An American Viticultural Area is a wine grape-growing region anywhere in the U.S. that can be defined as unique by evidence of geography, geology, weather and other facto