Cask strength (also known as barrel proof/barrel strength) is a term used by whiskey (often spelled "whisky" outside of Ireland and the United States) and rum producers to describe a whiskey or rum that has not been substantially diluted after its storage in a cask for maturation. The level of alcohol-by-volume (ABV) strength for a cask strength whiskey or rum is typically in the range of 52–66% ABV.