A realm, often referred to as a kingdom, is a significant political and territorial unit ruled by a monarch, such as a king or queen. It typically encompasses a defined geographic area and is characterized by its own laws, culture, and governance. Realms can vary in size and population, ranging from small principalities to vast empires. Historically, realms have played a crucial role in shaping societies and political structures. They often include various social classes and may have a feudal system, where land is exchanged for loyalty and service. Notable examples of realms include the United Kingdom, the Kingdom of France, and the Kingdom of Spain.