Tartness is a sharp, pleasantly sour taste that makes your mouth pucker slightly, like biting into a green apple or tasting fresh lemonade. Foods with tartness have an acidic quality that wakes up your taste buds without being unpleasantly sour.

You'll find tartness in many fruits: cranberries, raspberries, grapefruit, and unripe strawberries all have it. Yogurt has a natural tartness, which is why people often add honey or fruit to balance it out. A chef might add a squeeze of lemon to a rich pasta dish to give it tartness that cuts through the heavy cream.

The word can also describe someone's personality or way of speaking. A tart reply is sharp and a bit cutting, like when someone responds to a silly question with “Well, obviously,” in an impatient tone. This usage suggests wit with an edge to it, clever but not particularly warm.

In cooking, tartness often balances sweetness. Think about key lime pie: the filling needs tartness from the limes to keep all that sugar from being cloying. When a recipe works well, you can taste how the tartness and sweetness play off each other, each one making the other more interesting.