A sitemap is an organized model or diagram of a website's content, designed to help both users and search engines navigate the site. It can be an XML file or a webpage that lists all the pages, posts, and files on a website, along with additional metadata about each URL like when it was last updated and its importance relative to other URLs. Sitemaps are crucial for SEO as they help search engines find and crawl all the pages on a site. Especially for larger websites or those with a significant amount of multimedia content, a sitemap ensures that search engines can more efficiently discover all relevant pages.