A "kingdom" in biology is a classification of living things. Organisms belong to one of six kingdoms of life. The current kingdoms are the Archaebacteria, Eubacteria, protists, fungi, plants and animals.
At one time, only five kingdoms existed, with the Archaebacteria and Eubacteria being placed in one kingdom: Monera. This single kingdom exhibited so much diversity that it has since warranted division into two kingdoms.
The Archaebacteria are bacteria that live in inhospitable regions of the world, such as hot thermal vents. The Eubacteria consists of the other types of bacteria, many of which have contact with humans. The protists are single-celled organisms that can usually move on their own. The fungi consist of organisms that are single celled, have cell walls and obtain their food through absorption of nutrients. Plants are multicellular organisms that can make their own food through the process of photosynthesis. Animals are multicellular organisms that must obtain their nutrients from consuming other organisms.