The highest level of classification in biology that contains all the others is the Domain. In the biological classification hierarchy, there are several ranks used to categorize living organisms, starting from broad categories and becoming more specific.
The three main domains of life are Archaea, Bacteria, and Eukarya. Each of these domains encompasses various kingdoms, phyla, classes, orders, families, genera, and species. For example, all of the bacteria are contained within the domain Bacteria, while all animals, plants, and fungi belong to the domain Eukarya. Therefore, the domain is the most inclusive classification level and serves as the umbrella under which all life forms can be organized.