Faceted search is a technique for accessing a collection of information represented using a faceted classification scheme.
In a faceted classification scheme, each object or document can be classified based on multiple facets that represent independent ways of describing it. For example, the facets in a product catalog include category, brand, price, etc. The facets in a library catalog include subject, author, time period, etc. Faceted classification represents the fact that, as David Weinberger says, Everything is Miscellaneous, and it is artificial (if not impossible!) to arrange a large, diverse collection into single, pre-determined, hierarchy or taxonomy.