noun, plural: domains
(2) (zoogeography) A major faunal area of the earth's surface.
(3) (anatomy) A place in or a division of the body or a part of the body, as abdominal region.
(4) (molecular biology) A part of a molecule or structure with common physico-chemical features or properties, as in polar domain, atp-binding domain, helical domain, etc.
(5) (general) A realm of knowledge, thought, responsibility, etc., as the domain of science.
In biological taxonomy, a domain is the highest order of life classification, even higher than a Kingdom. Carl Woese introduced a three-domain system of classification in 1990 where organisms are divided into three domains: Archaea, Bacteria and Eukarya. Both the Domain Bacteria and Domain Archaea include prokaryotic organisms whereas the Domain Eukarya includes all eukaryotic organisms.