What is the difference between a scotch and a whiskey?

There is NO difference. Scotch IS whisky. Scotch is a nickname for whisky made in Scotland. On every bottle of whisky made in Scotland the label says 'Scotch Whisky' rather than 'Scottish Whisky'. The Word 'Scotch' simply means where the product is made i.e. Scotland.

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Scotch is a tradename and must meet requirements for ingredients, distilling, aging and blending to be called "Scotch". Whiskey is more generic referring to any distilled drink made from grain MASH, fermented and then distilled one, two or three times then stored in charred wooden barrels to "age" the whiskey and gain its brown color. In some cases the aging process is skipped as in the production of "moonshine", which techically could be called young unaged whiskey.