ullage

The amount of liquid within a container that is lost, as by leakage, during shipment or storage.

The amount by which a container, such as a bottle, cask, or tank, falls short of being full.

In com., the wantage of a cask, or the estimated measure of the empty part of a cask of liquor.

The amount which a vessel, as a cask, of liquor lacks of being full; wantage; deficiency.

In a wine bottle, the empty space between the cork and the top of the wine.

In a cask or barrel, the empty space, occupied by air, that is created by not completely filling the cask or barrel

The topping-up of such a barrel with fresh wine

In an industrial setting, the empty space in a tank, such as for fuel

the amount that a container (as a wine bottle or tank) lacks of being full