Whiskey has been around from 500-1000 years. It is distilled in oak casks which give each whiskey it's unique color and aroma, this is where it ages. Whiskey is made from various grains like barley, wheat, corn and rye. The word itself derives from the Latin aqua vitae, meaning "water of life".
Scotch whisky or simply "Scotch" is by international law a distilled product of Scotland, matured for a three year minimum in wooden oak casks. Canadian, Irish and Japanese whiskeys are of a similar description but to their own homeland.
Malt whisky is made using malted barley. Single malt is from a single distillery (not single cask unless specified). Grain whiskey is made from other grains aside from but including barley.
Blended whiskey is a cheaper blend of several whiskies.
American whiskey is aged for a minimum of 2 years in oak casks and comes under several categories; Bourbon (mostly corn/maize), Rye (minimum 51% rye), Corn (minimum 80%) and Tennessee whiskey.
Both "whiskey" and "whisky" mean the same although, the country of production or the company making the whiskey defines how it is spelt, almost on a per-product basis.