What is noindex?

A directive telling search engines not to show a page in results.

noindex is a robots meta tag or X-Robots-Tag HTTP header that asks search engines to keep a page out of their results. Search engines must be able to crawl the page to see it, so a page blocked in robots.txt can't be reliably de-indexed with noindex. Use it for thin, duplicate or private pages you still want people to reach.