Taxonomy is the practice and science of classification. The word finds its roots in the Greek, taxis (meaning 'order', 'arrangement') and nomos ('law' or 'science'). Taxonomy uses taxonomic units, known as taxa (singular taxon).

In addition, the word is also used as a count noun: a taxonomy, or taxonomic scheme, is a particular classification ("the taxonomy of ..."), arranged in a hierarchical structure. Typically this is organised by subtype-supertype relationships, also called parent-child relationships. In such a subtype-supertype relationship the subtype kind of thing has by definition the same constraints as the supertype kind of thing plus one or more additional constraints. For example, car is a subtype of vehicle. So any car is also a vehicle, but not every vehicle is a car. Therefore, a thing needs to satisfy more constraints to be a car than to be a vehicle.

Taxonomy is the technical term for the guiding principles behind the organisation of information—a key concern for Web developers. Every Web developer should know how to harness the basic principles of taxonomy to design a logical, organised, efficient Web infrastructure. By understanding information taxonomy and using it to optimise Web sites, Web developers can maximise the value and capability of their work.

The two key aspects of information taxonomy are taxonomy structure and taxonomy view. Taxonomy structure provides a classification schema for categorising content within the content management process. Taxonomy view is a conceptual model illustrating the types of information, ideas, and requirements to be presented on the Web. It represents the logical grouping of content visible to a site visitor and serves as input for Web site design and search engineering. Together, these concepts can guide your Web development efforts to maximise return on investment. Build it right, and they will come.