A no-index tag is an HTML tag used to instruct search engines not to index a specific page. This means that the page will not appear in search engine results. It's typically used on pages that aren't meant to be publicly searchable, such as login pages, thank you pages, or duplicate content.
By adding the no-index directive to a page, webmasters can prevent certain pages from affecting their website’s SEO, ensuring that only the most relevant and important pages are indexed and ranked. This tag is placed in the section of the page's HTML code, like this:
<meta name="robots" content="noindex">