Meta tag or X-Robots-Tag header?
They do the same thing. The meta tag only works in HTML pages. The header works for any file, including PDFs, images and feeds, and is the only option when you can't edit the page template. Google and Bing read both; if they disagree, the most restrictive rule wins.
Rules that trip people up
noindexneeds the page to be crawlable. If robots.txt blocks the URL, crawlers never see the tag and the page can stay indexed. See Indexed, though blocked by robots.txt.nofollowhere applies to every link on the page. For a single link userel="nofollow"on that link.name="googlebot"rules apply to Google only, and are added to anyname="robots"rules on the same page.- There is no
indexorfollowto switch on: it is the default. Leaving the tag out has the same effect.
Found a noindex you didn't expect in Search Console? The Excluded by 'noindex' tag guide lists where it usually comes from.
The tag is built in memory from what you tick. Nothing is fetched or stored.