A kingdom is a large area of land ruled by a king or queen. It is often part of a larger political structure, such as a country or an empire. Kingdoms can vary in size and population, and they may have their own laws, customs, and cultures. Historically, many kingdoms were established through conquest or inheritance. In biology, the term "kingdom" refers to a major category used to classify living organisms. The Five Kingdoms system includes Animalia (animals), Plantae (plants), Fungi (fungi), Protista (single-celled organisms), and Monera (bacteria). Each kingdom groups organisms based on shared characteristics and evolutionary relationships.