Whisky is alcohol distilled from grain (and often sugar is mixed in). Whisk
ey is the same, just the "Scotch English" spelling. Bourbon refers to the American style whisky, usually stronger, sweeter and less refined. Scotch is just whisky made in Scotland, no better than anything else by default, but generally seems smoother. Irish whisky seems less complex than Scotch or bourbon, a little more watery- but it's all to the drinkers taste.
"Single Malt" is whisky made from one type of grain only, not blended with another batch of whisky. Blends are just that, a blend of different grains and/or whiskies distilled from various distilleries.
Water, ingredients, aging and distilling techniques account for the differences in tastes. I prefer the "peat" tasting whiskies.. the most affordable one with good and consistent taste, to me, is McClelland Islay.