This information came via comments posted on an old thread, here. Go there if you want to get deep into some American whiskey esoterica.
It's about to get geeky over here too.
Most striking is a statement contained in Canada's Food and Drug Regulations (C.R.C., c. 870), which define different kinds of alcoholic beverages, in this case Tennessee whiskey.
"Tennessee whisky...is a straight Bourbon whisky produced in the State of Tennessee and manufactured in the United States as Tennessee whisky in accordance with the laws of the United States applicable in respect of Tennessee whisky for consumption in the United States."
That's a mouthful and, legally, it only applies within Canada, but it's interesting because it codifies the definition of Tennessee whiskey, something the United States Treasury Department's Tax and Trade Bureau (TTB) has never done.
TTB is keeper of the Standards of Identity for Distilled Spirits, which is the law of the land in terms of how distilled spirits are defined in the USA.
Note that the Canadian regulation does not define Tennessee whiskey as "straight bourbon whiskey that has been filtered through charcoal prior to barrel entry," which is what makes Tennessee whiskey unique according to the makers of Jack Daniel's.
Brown-Forman's Jack Daniel's and Diageo's George Dickel are the only Tennessee whiskeys, except for some emerging micros, but Jack is the best-selling American whiskey in the world and George is no slouch either.
The background for this is that the United States has trade agreements with various countries, such as Canada and Mexico, and entities such as the European Union, to recognize certain distinctive national products. In the North American Free Trade Agreement (NAFTA), for example, we recognize Canadian whisky and Tequila as distinctive products of Canada and Mexico, respectively, and they recognize bourbon whiskey and Tennessee whiskey as distinctive products of the United States.
NAFTA's wording is similar to the Canadian rule: "Tennessee Whiskey...is a straight Bourbon Whiskey authorized to be produced only in the State of Tennessee."
So even though TTB has never defined Tennessee whiskey, the U.S. government has, albeit indirectly, which should help you shut up a few know-it-alls and maybe win a bar bet or two.
It's also potentially significant for the micro-distilleries in Tennessee who want to make Tennessee whiskey because it puts them on notice that, contrary to that 2009 post, Tennessee whiskey isn't any whiskey made in Tennessee. The whiskey must meet all of the requirements for straight bourbon whiskey and be made in Tennessee to qualify.