Definition:
Google Sitemaps is a webmaster tool developed by Google to help streamline the submission of web pages to their search engine. Submitting a sitemap allows search engines to have a complete list of every webpage associated with your
website, and that is very important for ensuring site visibility.
Yahoo! also developed a similar tool called Yahoo! Site Explorer to allow webmasters to submit a complete listing of their web pages to the Yahoo! search engine. Both submissions utilize the sitemaps.org XML protocol standard.
See also Yahoo! Site Explorer.