A site map (or sitemap) is a list of pages of a web site accessible to crawlers or users. It can be either a document in any form used as a planning tool for web design, or a web page that lists the pages on a web site, typically organized in hierarchical fashion. This helps visitors and search engine bots find pages on the site.
XML is a document structure and encoding standard used, amongst many other things, as the standard for webcrawlers to find and parse sitemaps.
Example: