What wiskeys are bourbon?

Straight Bourbon whiskey is a type of whiskey (of course). Whiskey is a type of alcoholic drink made from cereal grains, distilled to strong spirit strength, and usually aged in barrels.

Bourbon is a very specific type of whiskey. It must be made in the US. The grain used must be at least 51% corn (maize). It must be aged in never-before-used white oak barrels that have been charred on the inside. It can't be distilled to over 80% alcohol by volume, and has to be barreled at less than 62.5% ABV. Additionally, for the Word "straight" to be on the label, it must be aged at least two years.

The flavored come from a combination of the grain used (corn gives bourbon a bit of sweetness), the lower distilling proof (higher proofs remove more of the grain flavors) and the new charred wood (allows for quicker aging and stronger flavors).

In practice most bourbons have even more corn than that, usually about 75%, with rye and malted barley making up the rest. Some have a lot more rye (but still less than the corn), as it gives a sharper, spicier flavor. Some use wheat instead of rye, which has the opposite effect as rye.

And just because its a popular misconception, there is absolutely NO requirement that bourbon be made in Kentucky!