Solr supports faceted searching. Faceted searching is a very useful extension to basic search functionality that allows you group search results in useful ways and perform simple analyses of database content. For an introduction to Solr's faceted search functionality and how to use it, see http://wiki.apache.org/solr/SolrFacetingOverview.
In order to use faceted searching with the Content Store you must enable it as follows:
Add the following line to configuration-root
Restart the application server.
Re-index the search engine in order to enable faceted search for existing content items.
Note that re-indexing may take a long time.