Ghost content—archived pages, forgotten staging sites, or remnants of a site...

https://cashnuyn401.theglensecret.com/what-are-mirrors-and-why-do-they-keep-my-old-pages-alive

Ghost content—archived pages, forgotten staging sites, or remnants of a site migration—often resurfaces in search results, hurting your current rankings. This happens when legacy caches remain indexed long after you’ve updated your site