What characteristic distinguishes bourbon from all other whiskeys?

The defining characteristic that distinguishes bourbon from all other whiskeys is that it must be produced in the United States. This geographical requirement is fundamental to the classification of bourbon. The U.S. has specific legal definitions concerning bourbon production, which include not only the place of origin but also the ingredients and production methods.

While aging and distillation proof are important aspects of bourbon's quality and production processes, they do not set it apart from other types of whiskey in the broader context. Furthermore, the grain composition for bourbon allows for a mix of corn and other grains, not just barley, which is a key differentiator for other whiskey types.

Overall, the stipulation that bourbon must originate from the United States is crucial, as it establishes the unique identity and heritage of this style of whiskey within the global spirits industry.