A duchy is a territory or domain ruled by a duke or duchess. Historically, duchies were significant political units in medieval Europe, often associated with nobility and feudal systems. They could vary in size and importance, sometimes encompassing entire regions or smaller areas within a kingdom. Duchies played a crucial role in the governance and administration of lands. They often had their own laws and customs, and the duke or duchess held considerable power over their subjects. Notable examples include the Duchy of Cornwall and the Duchy of Lancaster, which are still relevant in the United Kingdom today.