When you buy a French Chablis, it will be made only from Chardonnay grapes grown in a small district in France, because that is required under French law.
Likewise, when you buy a Sancerre, it can only be a sauvignon blanc from the eastern Loire Valley; a Beaujolais can only be made from the Gamay Noir a Jus Blanc grape grown in a district of Burgundy, and a port only from Portuguese grape varieties and made in Portugal.
It has been about 15 years since the United States belatedly agreed to recognize such wine terms as protected place names because they are actual regions in Europe. It's kind of like "Parmigiano Reggiano," which can only be made in certain Italian districts, though "parmesan" is an Americanized version that's widely used — and one that gourmets usually hate.
Updated: Tue Feb 08, 2022