A bung or stopper is a truncated cylindrical or conical closure to seal a container, such as a bottle, tube or barrel. Unlike a lid which encloses a container from the outside without displacing the inner volume, a bung is partially inserted inside the container to act as a seal.
A rubber stopper is sometimes called a rubber bung, and a cork stopper is called a cork. Sometimes bung stoppers used for wine bottles are referred to as "corks", even though made from another material.
The most common every-day example of a bung is the stopper of a wine bottle. Bungs are used to seal the bunghole of barrels. Other bungs, particularly those used in chemical barrels, may be made of metal and are screwed into place via threading.