From the FAQ at StraightBourbon.Com -- and they should know:
1. What is bourbon?
There are strict laws governing just what a Bourbon must be to be labeled as such. For example, at least 51 percent of the grain used in making the whiskey must be corn (most distillers use 65 to 75 percent corn). Bourbon must be aged for a minimum of two years in new, white oak barrels that have been charred. Nothing can be added at bottling to enhance flavor, add sweetness or alter color.
Download the BATF regulations governing bourbon here.
5. Why is this whiskey called bourbon?
It takes its name from Bourbon County, located in the central Bluegrass region of Kentucky. It was formed from Fayette county in 1785 while still a part of Virginia and named to honor the French Royal Family and was once the major transshipment site for distilled spirits heading down the Ohio and Mississippi rivers to New Orleans. Barrels shipped from its ports were stamped with the county's name, and Bourbon and whiskey soon became synonymous.
6. Is Jack Daniel's a bourbon?
Jack Daniel's, is not considered a bourbon because it is charcoal-mellowed -- slowly, drop by drop, filtered through sugar-maple charcoal -- prior to aging, which many experts say gives it a different character. The process, called the Lincoln County Process, infuses a sweet and sooty character into the distillate as it removes impurities. But up to and after the charcoal filtering, the Jack Daniel's production is much the same as any other Bourbon. Jack Daniel's and George Dickel are two fine Tennessee Whiskeys though neither can be called bourbon.