To capacity, lid off, time for the remaining liquid

• Liquid lost from a container
• Amount lacking to make a full cask
• Empty portion of a bottle
• Amount needed to fill a cask
• Unfilled part of a wine container
• Amount needed to make a full cask

Wikipedia Word definitions in Wikipedia
Ullage or headspace is the unfilled space in a container, particularly with a liquid.

WordNet Word definitions in WordNet
n. the amount that a container (as a wine bottle or tank) lacks of being full

Wiktionary Word definitions in Wiktionary
n. 1 In a wine bottle, the empty space between the cork and the top of the wine. 2 In a cask or barrel, the empty space, occupied by air, that is created by not completely filling the cask or barrel 3 The topping-up of such a barrel with fresh wine 4 In ...