Whiskey
Is a distilled spirit, made from grain, and aged in oak casks.

There are two different spellings of Whisk(e)y. With, and without the 'e'. And how it is spelled will depend on where it comes from. When it is spelled 'Whiskey', it either comes from Ireland, or America. When it is spelled 'Whisky', that means it comes from either Scotland or Canada. But it is also important to note that this is just by "practice" and is not a legal requirement. For example "Maker's Mark", a bourbon whiskey from America uses Whisky on their label.

Irish Whiskey

is a blend of grain and barley malt whiskies. Bushmills distilling house dates back to 1608, making it the oldest distiller in the world. Irish whiskey is made essentially the same way as Scotch whiskey, except that there is no peat included in the process, and so it doesn't have the smokey flavor of Scotch whisky. Like Scotch, Irish whiskey comes in two categories, "single malt" and "blended", with the same definitions being applied.

Scotch Whisky

is made the same as Irish whiskey, except that they derive a unique peaty and smoky flavor from the process of drying the malt barle over peat fires. There are essentially two different types of scotch, "single malt" and "blended".

A single malt scotch is one that comes from a single distillery. It does not mean that it comes from a single barrel, or even from a single year. A blended scotch on the other hand can be a blend of scotches from different distilleries, as well as with additional "neutral grain spirits" added to balance the product and achieve a specific flavor. Another, less common, category is "pure malt", which is a blending of scotches from different distilleries, but unlike a blended scotch, there are no non-scotch products added.

American Whiskey

Bourbon is the most poular and is made with at least 51% corn, the remainder is made up of barley, rye, or wheat. Bourbon must be aged for at least 2 years in new charred oak barrels, but most bourbons will spend at least 4 years in the barrel. The name Bourbon comes from Bourbon county in Kentucky, and while (currently) all but one Bourbon is made in Kentucky, it can be made anywhere in the United States and still legally be called Bourbon.

Rye is made with at least 51% rye, the remainder is made up of barley and corn. Like bourbon, rye must be aged for at least 2 years in new charred oak barrels. While you might find some people referring to "Canadian whisky" as Rye, it is not the same thing. Canadian whisky might contain rye, but it is not made like American rye. When a drink calls for rye whiskey, it would be better to substitute bourbon instead of Canadian whisky.

Corn whiskey: is the least produced of the three, and is made up of at least 80% corn, with the remainder consisting of barley and rye.

Canadian Whisky

Is almost always blended, and often uses rye as the primary component, although this is not dictated by legal standards. Usually it is lighter and smoother then the other styles.