Ullage is the airspace between the wine barrel and its lid, or the bottled wine and its cork. (If you really want to split hairs, ullage is what isn't between a wine barrel and its lid—that is, evaporated wine.) Excessive ullage may be an indication that the cork is leaking or that the wine is evaporating due to high heat and/or low humidity. Solutions include: 1) drinking the wine now, or 2) recorking and topping-up the wine, then storing it in a proper environment. If the ullage is an inch or more, it's time to start worrying. By contrast, in brandy making, ullage is affectionately referred to as "the angel's share," a heady aroma that leaves you slightly tipsy during your guided tour of the barrel storage room.