Noindex
An instruction, in a robots meta tag or an X-Robots-Tag header, telling search engines not to include a page in their results.
A noindex page can still be visited, but it won't be found in search, and AI assistants that search the web are unlikely to see it. On a paid placement, a noindex tag quietly hides the article you paid for, so it is worth checking.
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Related: Canonical URL · rel="sponsored"