The Noindex Tag is an instruction added to a webpage's code that tells search engines not to list that page in their search results. Website owners use this tag to keep certain pages, such as duplicate content, private information, or low-value pages, out of public search listings. The tag is placed in the page’s HTML and is recognized by most major search engines. Using the Noindex Tag helps control which parts of a website are visible to the public and can improve overall site quality by preventing irrelevant or sensitive content from appearing in search results.