A kingdom in biology is the second-broadest category in the system that is used to classify all organisms based on their fundamental characteristics and evolutionary relationships. Kingdoms are a subdivision of domains, the broadest category, and they, in turn, are subdivided into phyla.
The domain eukarya, which contains organisms whose cells have a membrane-bound cell nucleus and organelles, includes four kingdoms: animals, plants, protista (protozoans, slime molds, and some algae) and fungi (mushrooms, molds, and yeasts). The other domains, archaea and bacteria, although extremely diverse, do not contain formally designated kingdoms but can be further classified into phyla and subdivisions thereof.