The Site Map Module enables a Drupal website to have a dynamically generated site map.
A site map (or sitemap) is a web page that lists the pages on a web site site, typically organized in hierarchical fashion. This helps visitors, and search engine bots, to find pages on the site.
Source: http://en.wikipedia.org/wiki/Site_map
When the Site Map Module is installed it can be configured to display:

• A hierarchy of all menu items
• Listing of all terms grouped by vocabulary
• Listing of all nodes or selected nodes
• Or any combination of the above

Most Drupal websites have a link to a site map in the header or footer of the website. And generally, this is also available via the URL:

• http://<website>/sitemap or
• http://<website>/site-map