Search engines must be able to crawl a page to see its noindex directive, so do not block noindexed pages in robots.txt.
Noindex is the right tool to keep thin, duplicate or private pages out of search results.
SEO glossary
A directive, set in a meta robots tag or an X-Robots-Tag HTTP header, that tells search engines not to include a page in their index.
Search engines must be able to crawl a page to see its noindex directive, so do not block noindexed pages in robots.txt.
Noindex is the right tool to keep thin, duplicate or private pages out of search results.