Original: While Duff Beer comes in several varieties, it is revealed on a Duff Brewery tour in "Duffless" that regular Duff, Duff Light, and Duff Dry are the same beer, although Homer and Barney apparently remain oblivious to the fact.
Simplified: Duff Beer is a fictional alcoholic drink shown in the animated television series The Simpsons. Duff Beer is known to be Homer Simpson's favorite drink and has a mascot known as Duffman.