In general, whiskey (or whisky) is a variety of distilled liquors made from fermented grain mash and aged in wooden containers, usually made of oak. Commonly used grains are barley malt, corn, and rye. So, what distinguishes different whiskey types? Simply put, the different types of whiskey are based on the type of grain used in the distillation process and where it was produced.
Technically speaking, one of the factors that makes whiskey unique is contact with wood. Whiskey that has been in contact with the wood for a few seconds is still considered aged whiskey in the United States, as contact with wood is a way of determining age. Other types of whiskey like bourbon, Japanese, Irish, Canadian, and Scotch all have their own rules.
Bourbon for example needs to be aged in new burnt oak barrels and pure bourbon must do this for a minimum of 2 years. Scotch cannot be labeled as " aged whiskey" until it has been aged for three years and one day in Scotland.