You know how champagne can only be labelled as such if it's from a certain region of France? Well, bourbon is sort of the same. It must be made in the US. Many people think it need come from Kentucky, though this isn't technically true. Bear with me - recall I'm a lawyer and I actually like technicalities (I'm weird like that.). Jim Beam does a nice job of explaining what bourbon is in this link:
Bourbon, like scotch, is a type of whiskey. But not all whiskey is bourbon. No scotch is bourbon. And Canadian whiskey? Not bourbon at all. Don't ask about Irish whiskey. It's not bourbon, either.