In winespeak, firm is that sought-after plateau between soft and tough. A white wine, for example, is considered flawed if it has too much acidity (making its bite unpleasantly strong) or not enough (in which case it's flabby). The goal of the winemaker is to achieve the perfect balance of acidity, so that the wine is neither wimpy nor brawny but attractively firm. The same goes for red wine, though its firmness derives from tannic astringency rather than acidity.