the hole in the head of a cask, keg, or barrel. It can also refer to the hole in the belly or bilge of a cask and to the devices that seal those holes. The average size of a cask or barrel bung is 1 15/16 inch, although some breweries have used smaller sizes in North America for Hoff-Stevens and Golden Gate kegs.

When referencing the bung as a closure, it is a hard nylon, rubber, or wood stopper used to plug the hole in the head or belly of a cask or keg. The shape is generally a slightly truncated cylinder, and it is usually hammered in to be flush with the container. In traditional English cellaring the bung refers solely to the hole in which the keystone is inserted in the cask head and the shive boss is in the belly of a cask.

See also barrel, cask, golden gate kegs, hoff-stevens kegs, and keg.