Whisky or whiskey is a type of alcoholic beverage distilled from fermented grain mash. Different grains are used for different varieties, including barley, malted barley, rye, malted rye, wheat, and maize (corn). Most whiskies are aged in wooden casks, made generally of oak), the exception being some corn liquors.

Whisky is a strictly regulated spirit worldwide with many competing denominations of origin and many classes and types. The unifying characteristics of the different classes and types are the fermentation of grains, and the practice of distilling the spirit down to a maximum of 80% alcohol for corn and 90% alcohol for other grains, prior to adding water, so as to retain some of the flavor of the grain used to make the spirit and prevent it from being classified as grain neutral spirits or vodka. Whisky gains as much as 60% of its flavor from the type of cask used in its aging process.[citation needed] Therefore further classification takes place based upon the type of wood used and the amount of charring or toasting done to the wood. Bourbon whiskey for example is legally required to be aged in charred new oak barrels, whereas quality Scotch whiskies often used the partially spent barrels from Bourbon production to induce a slower maturation time, adding additional subtle nuance.

With few exceptions, the spelling is Scottish, Canadian, and Japanese whisky (plural: whiskies), but Irish and American whiskey (whiskeys).