The X-Robots-Tag header is an HTTP response header used by website owners and developers to control how search engines index and display web content. Unlike the traditional <meta name="robots"> tag, which is placed within the HTML of a page, the X-Robots-Tag header is set at the server level and can be applied to any file type, including PDFs, images, and other non-HTML resources. By specifying directives such as noindex, nofollow, or noarchive, this header instructs search engine crawlers on how to handle the content, helping to manage a site's visibility and privacy in search results.