Bourbon is a style of American whiskey, and gets its name from the area in which it was originally being shipped from, which in the 1700's (when bourbon was first being produced) was known as "Old Bourbon" (named after "The House of Bourbon", a european royal house), and is now Bourbon County in Kentucky. They key defining requirement that differentiates bourbon from other whiskies is that it is made primarily from corn. It can be made anywhere in the United States (although the vast majority is made in Kentucky), It must be aged in new charred oak barrels. It must be distilled to no more than 80% abv (alcohol by volume). When put into the barrel for aging, it must not be more than 62.5% abv. When bottled it must be at 40% abv or more. And while there aren't any specific aging requirements, it must recieve some barrel aging.