noun, plural: kingdoms
Historically, kingdom is the highest taxonomic rank, or the most general taxon used in classifying organisms. However, in the new three-domain system introduced by Carl Woese in 1990, the domain is the most general taxon, and kingdom is only next.
The five-kingdom taxonomic classification of the world's biota into Kingdom Animalia, Plantae, Fungi, Protista, and Monera as proposed by Robert Whittaker in 1969 has become a popular standard of classifying organisms. It became the basis for newer multi-kingdom systems such as the six-kingdom system of Carl Woese and colleagues in 1977.
The five biological Kingdoms (by Robert Whittaker):
Kingdom Monera: the most primitive of the five kingdoms that includes all the bacteria, also called monerans, which are single-celled prokaryotic organisms. (In six-kingdom system, Kingdom Monera is split into two kingdoms: (1) the Eubacteria, which are all bacteria apart from the archaebacteria, and (2) the Archaebacteria, which are single-celled organisms that live under extreme environmental conditions and have distinctive biochemical features)
Kingdom Fungi: includes multicellular, non-photosynthetic, saprotrophic organisms such as slime moulds, mushrooms, smuts, rusts, mildews, moulds, stinkhorns, puffballs, truffles and yeasts that absorb food in solution directly through their cell walls and reproduce through spores
See also: taxonomy.