The noindex meta tag is an HTML element that instructs search engine crawlers not to index a specific webpage or follow its links. Webmasters may use the noindex tag to prevent certain pages from appearing in search engine results, such as thank-you pages, login pages, or duplicate content. If a webpage contains a noindex tag in its HTML code, search engines like Google will honor this directive and refrain from indexing the page's content. This means that even if the page is accessible to users, it won't show up in search results, effectively hiding it from organic search traffic.