Wines get their sweetness from residual sugar (RS), which is leftover glucose from grape juice that wasn’t completely fermented into alcohol. However, our sense of taste picks up sweetness in varying levels.
Most still wines fall into the dry category, even though our taste buds might tell us differently. There also “off-dry” wines, that are included in this section. “Off-dry” is a popular term to describe wines with a touch of residual sugar, which can be anywhere from 2–3 grams of residual sugar per 5 oz pour. Most off dry wines are white wines, although on rare occasions you can find high quality Italian red wines that fall into the off dry category. High acidity wines like Riesling will taste more dry than a lower acidity wine (like Viognier) at the same actual sweetness level.
Lastly, some whites are always sweet: Sauternes and "late-harvest" bottlings of grapes such as Riesling and Chenin Blanc are examples.