What are an index and a no-index tag?

Noindex means that a web page shouldn't be indexed by search engines and therefore shouldn't be shown on the search engine's result pages. nofollow means that search engines spiders shouldn't follow the links on that page. You can add these values to your robots meta tag.

When you add a noindex tag to a page, it lets search engines know that although it can still crawl the page, it can't add the page to its index.