An XML sitemap is a file that helps search engines like Google understand the structure of a website. It lists all the important pages, making it easier for search engines to find and index them. This is especially useful for larger websites with many pages or for those that frequently update their content. By providing a clear roadmap of a website's content, an XML sitemap can improve a site's visibility in search results. It can also include additional information, such as how often pages are updated and their importance relative to other pages on the site.