Whisky (or “whiskey”; see update below) refers to alcoholic beverages that are derived from grains and aged in oak casks. Scotch whisky (or simply Scotch) refers specifically to whiskey produced in Scotland, and which is distilled primarily from malted barley. Bourbon, in contrast, is an American whisky that is at least 51% derived from corn. Canadian, or rye, whiskey typically is 51% or greater rye alongside other grains. And, of course, those with small home distilleries and unspecified grain percentages have a name, too: moonshine.
I am far from a drinker, but I do enjoy a nice glass of Scotch on the rocks, Lagavulin in particular. And as of this past weekend, I’m going to start exploring the world of bourbon as well (Knob Creek was a good introduction). Just don’t reprimand me if you see me ordering it before dinner instead of after.
Update: the wise and observant Ken Schlager points out that the correct spelling (per AP style) is “whiskey” unless referring to “Scotch whisky.” Duly noted and repaired.