Duff is a term that refers to the leftover residue from brewing beer, specifically the spent grains and hops that remain after the liquid has been extracted. It is often used in the context of beer production and can be a valuable byproduct for various uses. In addition to its brewing context, Duff is also known as a character from the animated television show The Simpsons. Duff Beer is the fictional beer brand consumed by many characters in the series, often depicted as a popular and low-quality beverage enjoyed by the show's protagonist, Homer Simpson.