• Malt is whisky made entirely from malted barley and distilled in an onion-shaped pot still.
• Grain is made from malted and unmalted barley along with other grains, usually in a continuous“patent” or “Coffey” still. Until recently it was only used in blends, but there are now some “Single Grain” scotches being marketed.

Malts and Grains are combined in various ways

• Vatted malt is blended from malt whiskies from different distilleries. If a whisky is labelled “pure malt” or just “malt” it is almost certain to be a vatted whisky. This is also sometimes labelled as “Blended Malt” whisky.
• Single malt whisky is malt whisky from a single distillery. However, unless the whisky is described as “single-cask” it will contain whisky from many casks, and different years, so the blender can achieve a taste recognisable as typical of the distillery. In most cases, the name of a single malt will be that of the distillery (The Glenlivet, Bushmills, Yoichi), with an age statement and perhaps some indication of some special treatments such as maturation in a port wine cask.
• Pure pot still whiskey refers to a whiskey distilled in a pot-still (like single malt) from a mash of mixed malted and unmalted barley. It is exclusive to Ireland.
• Blended whiskies are made from a mixture of Malt and Grain whiskies. A whisky simply described as Scotch Whisky or Irish Whiskey is most likely to be a blend in this sense. A blend is usually from many distilleries so that the blender can produce a flavour consistent with the brand, and the brand name (e.g. Chivas Regal, Jameson Irish Whiskey, Canadian Club) will usually not therefore contain the name of a distillery. However, “Blend” can (less frequently) have other meanings. A mixture of malts (with no grain) from different distilleries (more usually called a vatted malt) may sometimes be referred to as a “Blended Malt”, and a mixtures of grain whiskies with no malts will sometimes carry the designation “Blended Grain”.

• Cask strength whiskies are rare and usually only the very best whiskies are bottled in this way. They are bottled from the cask undiluted. Rather than diluting, the distiller is inviting the drinker to dilute to the level of potency most palatable.

Whiskies do not mature in the bottle, only in the cask, so the “age” of a whisky is the time between distillation and bottling. This reflects how much the cask has interacted with the whisky, changing its chemical makeup and taste. Whiskies which have been in bottle for many years may have a rarity value, but are not “older” and will not necessarily be “better” than a more recently made whisky matured in wood for a similar time. Most whiskies are sold at or near an alcoholic strength of 40% abv.

source: Wikipedia