What’s the difference between “terroir,” “appellations” and “AVAs”?

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Dear Dr. Vinny,
What’s the difference between “terroir,” “appellations” and “AVAs”?
—Chuck, Celina, Ohio
Dear Chuck,
I love this question. All of these terms are reflective of the idea that where a grape is grown is important, but each of them is distinct.
The broadest and most abstract of these three is terroir, a term derived from the French word for earth, “terre.” It translates loosely as “a sense of place,” and it’s the idea that a wine’s character is influenced by where its grapes were grown—that wine can express the sum of dozens of variables, including soil, climate, topography and even bacteria and microbes in a specific site. The concept of terroir can also be applied to coffee, chocolate, tea, beef, cheese and anything else that’s influenced by where it’s raised or grown.
An appellation is a legally defined geographic area. At a minimum, an appellation on a bottle of wine lets us know where the grapes were grown. But each country has different rules for their appellations: Many European appellations, for example, dictate not just geographic boundaries but also which grapes are permitted and even certain vineyard and winemaking practices. There can’t be any Pinot Noir in a bottle of Bordeaux, and you won’t find any Merlot in a Burgundy.
AVA is the abbreviation for American Viticultural Area, and it’s basically the United States’ version of an appellation. As with appellations in other countries, it takes a lot of work to get an AVA officially recognized—petitioners must prove that the region is distinctive and has relatively uniform terrain, soil and climate, and the boundaries must be agreed upon. AVAs, however, do not restrict what types of grapes can be grown nor how the wines must be made.
AVAs and appellations can also nest within one another, for instance, the Pauillac appellation is within the Bordeaux appellation, and the Oakville AVA is within the Napa Valley AVA.
—Dr. Vinny