We can't think of any other topic that has caused so much confusion as Single Malt. Technically speaking, single malt scotch whiskey is just a single distillery product, not a single batch or single barrel product.
Single-grain Scotch whiskey differs only because it contains barley and other grains, usually wheat or corn. Again, single malt refers to products made in a single distillery, not products made from single grains. This should also better explain the single malt vs. blended debate.