Single Malt Whisky

Single malt whisky is whisky from a single distillery, made from only malted barley.

It's important to notice that single does not refer to the word malt here, as it would in an ordinary English sentence. Single refers to the distillery only! There are single malt whiskies made from different types of malted barley, confusingly enough! For example, Glenmorangie Signet is made from two types of malt. However, since it is all made from one single distillery, it's still a single malt whisky.

Glenmorangie Signet - a single malt made from two types of malt

Another important detail to notice is that the distillery may blend together casks in any way they like to make their single malt whisky. In fact, most single malts are made by blending large amounts of casks in order to create a certain flavor profile. As long as all whisky comes from the same distillery and is made from malted barley only, it's a single malt whisky.

Laphroaig 10 - made by blending, but not a blended whisky

There are some related terms that have special (and sometimes confusing) meanings as well:

Blended whisky
Blended malt whisky
Single grain whisky
Blended grain whisky
Single cask