UB is an expert and was asking for a definitive answer. The resulting lively discussion covered the terms and also their use and abuse by the industry. The last word and as good a definition as emerged was as follows fromu CK:

• A Single Malt is a Whisky made exclusively from malted barley, from one source (distillery). Not necessarily from a "single" production batch or even of the same age. Youngest age may be stated. E.g. Macallan, Laphroaig, etc...

• A Vatted Malt is a Whisky made exclusively from malted barley, usually mixed from whiskies from various sources (distilleries). Not necessarily of the same age. Youngest age may be stated. Also often simply stated as "Malt Whisky". E.g.: Poit Dhubh, The Bennachie.

• A Pure Malt is a Whisky made exclusively from malted barley. No indication of origin is given, thus it might either be a Single Malt or a Vatted Malt, and is commonly found on both. Not necessarily of a same age. Youngest age may be stated. E.g. Glenfiddich, Poit Dhubh, The Bennachie, are all Pure Malts (as are ALL Single or Vatted Malts). Pure does NOT mean that there is no caramel in it (!).

  Note that the Glenfiddich, while definitely being a Single Malt (from one distillery), is labeled "Pure Malt". There are also other examples of Single Malts labeled such. Apparently, in the past it was much more common to label Single Malts as Pure Malts, maybe because of the fact that the word "Pure" also projects some image of natural, unadulterated, unfiltered, etc... into the minds of the (average, [novice]) consumer whereas the word "Single" might not have that much positive association. Unfortunately, since it is possible to also label Vatted Malts as "Pure", this is now quite common. E.g. The Bennachie (before the company turned belly-up), where the label of that Whisky was at one time changed from "Vatted Malt" to "Pure Malt". Fortunately, it can be safely assumed that the market share for Vatted Malt is almost negligible as compared to either blends or mass-marketed Single Malts such as Glenfiddich or Glen Grant. In addition, there are now some more denominators not very clearly defined, but more-or-less used by consensus.

• Single-single, Single Cask, are Whiskies exclusively bottled from one cask. E.g. most IB bottlings (Blackadder, Cooper's Choice, etc...).

• Vintage Malt, Whisky of the same age. May be from different casks or production runs, though. Example: Vintage Islay Malt, Finlaggan. All Single Cask Bottlings are also Vintage Malts (even if the year is not stated), but not vice-versa.

• Cask Strength. While in the IB realm, this is often associated with "The" pure (?) whisky, as bottled straight from the cask, we must not forget that the industry bottles large batches adjusted to a specific strength (e.g. Glenfarclas 105), which means that it is NOT as it comes from the cask!

These are a good definition of what the terms should and usually do mean. Some bottlers however use 'pure' and 'vatted interchangeably and occasionally use 'pure' instead of 'single'. Caveat emptor. [jhb]