Wikipedia Article About Sauternes on Wikipedia
Sauternes is a type of dessert wine made from Sémillon, Sauvignon Blanc, and Muscadelle grapes that have been affected by Botrytis cinerea, also known as noble rot. This causes grapes to become partially raisined, resulting in extremely concentrated and distinctively flavored wines, typically with an arresting golden color. Sauternes is one of the few wine regions where infection with noble rot is a frequent occurrence, due to its mesoclimate. Even so, production is a hit-or-miss proposition, with widely varying harvests from year to year.
Wines from Sauternes, especially its flagship estate Château d'Yquem, can be very expensive, due largely to the very high cost of production. Barsac lies within Sauternes, and is entitled to use either name. Somewhat similar but less expensive and typically less-distinguished wines are produced in the neighboring regions of Monbazillac, Cérons, Loupiac and Cadillac.
Note that lower quality dessert wines and white wines, primarily American, are occasionally labeled as 'sauterne'.