A sitemap is a file, usually in XML, that lists the URLs on a site you want search engines to know about, optionally with hints such as when each page last changed. It does not force anything to be crawled or ranked, but it helps search engines discover pages, which is especially useful for large sites, new sites with few inbound links, or pages buried deep in the structure. A sitemap complements internal linking rather than replacing it. Submitting it through a search engine’s webmaster tools, and referencing it from robots.txt, makes discovery more reliable.
Glossary
Sitemap
A file listing a site’s URLs to help crawlers find them.