Use of Faceted Classification
http://www.webdesignpractices.com/navigation/facets.html

Adkisson, Heidi P.
Web Design Practices
2005

Abstract:

Unlike a simple hierarchical scheme, faceted classification gives the users the ability to find items based on more than one dimension. For example, some users shopping for jewelry may be most interested in browsing by particular type of jewelry (earrings, necklaces), while others are more interested in browsing by a particular material (gold, silver). “Material” and “type” are examples of facets; earrings, necklaces, gold, silver are examples of facet values.