With taxonomy we mean the keywords that you can link to the pages of your website. This can be done when creating or editing a page, in "Page Content and Options." This is especially useful when you use the search function to filter page content.
Create and organize a keyword list in the backend through Structure> Taxonomy> General Glossary.
Both taxonomy is used in both the Faceted Search paddlet and the Advanced Search pages paddlet. Use these tags as filters, which can help query search. These filters are displayed on the left side of the search page and can be turned on and off. The more keywords are checked, the more sophisticated the search results.
More explanation about Faceted Search can be found in the FAQ.