Taxonomy is the practice and science of categorization or classification. It is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. Taxonomy can be used to organize and index knowledge, such as in the form of a library classification system or a search engine taxonomy, so that users can more easily find the information they are searching for. Taxonomy is not limited to the classification of organisms, but can also refer to the categorization of things or concepts, as well as to the principles underlying such a categorization. Taxonomy organizes taxonomic units known as "taxa" (singular "taxon") . Taxonomy is different from meronomy, which deals with the categorization of parts of a whole. Taxonomy is used in various fields, including biology, computing, and web design. In biology, taxonomy is the branch of science that studies the naming, arranging, classifying, and describing organisms into groups and levels. Taxonomists identify, describe, and arrange species into classifications, including those that are new to science. Taxonomy provides the basis for a relatively uniform and internationally understood nomenclature, thereby simplifying cross-referencing and retrieval of information.