The No-Index tag is an on-page directive that instructs crawler bots not to add the webpage they encountered to their index.

This is used for things that you don’t want indexed for search, such as website login pages, as well as for content such as PPC landing pages, which are not optimized for organic search.

Be sure that all pages that you do not want indexed for search contain a No-Index tag, and are noted in your Robots.txt file & excluded from your site’s XML Sitemap.