Whisky or whiskey is a type of distilled alcoholic beverage made from fermented grain mash. Various grains (which may be malted) are used in different varieties, including barley, corn, rye, and wheat. Whisky is typically aged in wooden casks, generally made of charred white oak. Whisky is a strictly regulated spirit worldwide. It encompasses many national expressions and variations. The typical unifying characteristics of the different expressions and variations are the fermentation of grains, distillation, and aging in wooden barrels.