All Scotch whisky must be matured in Scotland for a minimum of three years before it is regarded as such. Strictly speaking there are two types of whisky currently produced in Scotland, malt whisky and grain whisky. From these two spirits we get the following types of whisky.
Whisky made from malted barley. Typically made in a batch process using copper stills.
This is whisky bottled from one malt whisky distillery. Many casks from this distillery may be married together to get the right flavour but as long as the whisky all comes from one distillery it is single malt.
Single cask malt
A bottling made from just one cask from a malt whisky distillery. These bottlings are limited to the number produced by any one cask and are thus usually more exclusive. Many of these bottlings will be seen at "natural" or "cask strength."
Blended Malt or Vatted Whisky
Sometimes, strangely, refered to as "Pure Malt" these whiskies are produced by the marrying together of malt whiskies from different distilleries. A vatted malt can comprise of the whisky from any number of distilleries.
This whisky is produced in a similar, but continuous, fashion to malt whisky but it is made from different cereals, mainly wheat and maize with only the smallest amount of barley required to help with the fermentation process.
Single grain whisky
As with single malt whisky this is the product of one distillery. Not very commonly produced as not regarded as very palatable although some interesting attempts have been released recently.
This whisky is made up of any mixture, ratio, of as many different grain and malt whiskies desired. Some blended whiskies may have as little as 3% malt whisky content where as others have as much as 60%.