All bourbon is whiskey, but not all whiskey is bourbon
If you sat down at a bar and someone simply handed you a shot of brown liquor, I wouldn’t blame you if you couldn’t tell whether it’s bourbon or whiskey. (Or didn't care, depending on how your day went.) The difference between bourbon and whiskey can be a little difficult to understand, since all bourbon is whiskey, but not all whiskey is bourbon. Either, of course, tastes great in a brunch punch or even your morning cup of coffee. But whiskey is a catchall term for distilled alcohol made from grain mash. That mash can be made of rye, corn, wheat, whatever grain that might be around. So when you talk about “whiskey,” you could be talking about scotch or rye whiskey or, of course, bourbon. But if you’re talking about bourbon, you’re talking about American booze. Bourbon is, in fact, “America’s native spirit,” according to a Congressional decree, dated 1964.
There are, however, plenty of whiskeys made in the United States that aren’t technically bourbon—and a whiskey’s geographic origin isn’t the only thing that makes it bourbon. The mash used to make bourbon must be at least 51 percent corn, though the recipe differs between distillers. Other types of whiskey might have more barley than corn, and scotch recipes generally have more malted grain than anything else. Bourbon must also, "be distilled to a maximum strength of 160 proof, bottled at a strength of at least 80 proof, and barreled for aging at no more than 125 proof," writes Natalie Wolchover for LiveScience.
The biggest difference between bourbon and whiskey production is the type of barrels in which the alcohol is aged. Bourbon must be aged in “new charred oak barrels,” according to the American Bourbon Association. Whiskey can be aged in used oak barrels; in fact, Ireland's Jameson Whisky is aged in used American bourbon barrels. (These barrels are fairly versatile, too. Starbucks recently released a limited run of coffee beans aged in used American bourbon barrels, though that coffee is woefully non-alcoholic.)
If you are drinking bourbon, chances are good that you're drinking Kentucky bourbon. According to the Kentucky Distillers' Association, approximately 95 percent of the world's supply of bourbon comes from Kentucky. But really, the only difference between Kentucky bourbon and any other type of American bourbon is that Kentucky bourbon is distilled and bottled in Kentucky.
You could also look for bottled in bond bourbon, if you're really set on drinking high-quality, American bourbon. Only American spirits can be labeled "bottled in bond," a designation that was created in the 19th century by politicians to ensure a high standard of American whiskey. As Tony Sachs writes for Serious Eats, "bottled-in-bond whiskeys had to consist of whiskey distilled entirely by one distiller at one American distillery in the same calendar year; they had to be aged at least four years under government supervision in secured federal buildings; and they had to be bottled at 100 proof (50% alcohol by volume)." Those definitions stay true to this day, and these bourbons are generally a good value.
You can't really go wrong with any bourbon, though. After all, it's just whiskey.