1. A spirit distilled from malted grain, especially barley or rye.
Whisk(e)y is a distilled alcohol made from fermented grain mash (barley, corn, rye or wheat). These different grains is what ultimately differentiates the different types of whisk(e)y.
Scotch is made from malted barley and must be made in Scotland.
Bourbon is distilled from at least 51% corn and is made in America, originating from Kentucky.
Rye whisk(e)y in America must have at least 51% of rye in it to be classified as a rye whisk(e)y. Rye whisk(e)y in Canada, however, does not require a particular percentage as long as some rye is present.
Irish whiskey is basically any whiskey made in Ireland.