Is there a difference between a “semi-dry” wine and an “off-dry” wine?

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Dear Dr. Vinny,
Is there a difference between a “semi-dry” wine and an “off-dry” wine?
—Caitlyn, Cape Town, S.A.
Dear Caitlyn,
Nope! “Semi-dry” and “off-dry” are two terms for the same thing. Dryness in wine has a technical definition: Wines with less than 10 grams of residual sugar per liter are considered “dry,” those with more than 30 grams per liter are “sweet,” and anything that falls between is considered “off-dry” or “semi-dry.”
Talking about sweetness in wine can be a complicated thing. Even though you might think that all wines that are technically dry taste dry, or all wines with more than 10 games of residual sugar per liter have at least a perceptible sweetness, that’s not always the case. A wine can be technically dry, but the flavors come across as ripe and even a little bit sweet. A semi-dry wine can still have plenty of acidity that makes the flavors seem fresher than candied.
To further muddle the situation, perception and tolerance for sweetness can vary from person to person. What might seem cloying to you might seem perfectly fine to my sweet tooth.
—Dr. Vinny