Mirror site
A mirror site is a full copy of a website hosted at another address, used for downloads, backups or access in other regions.
A mirror site is a copy of a website, or a large part of one, hosted at a different address. It has the same pages and the same content, kept in step with the original. Mirrors have honest uses: spreading the load of big downloads, keeping a site up when the main server fails, or serving people in a country where the main site is blocked or slow.
For SEO, a mirror is a duplicate of every page you have, and search engines have to decide which copy to show.
The SEO problem
When the same pages live at two addresses, search engines usually pick one to show and drop the other. If they pick the mirror, your main site loses visits it should have had. Links get split between the two copies too.
The fix is to tell search engines which copy is the original. Add a canonical link on each mirrored page pointing to the original, or keep the mirror out of the index with noindex. Google explains the options in its guide to duplicate URLs.
For example, say Harrow & Pine runs a copy of its site at an old domain, left over from before it changed its name. Nobody remembers it's there. Search engines find both, and for some products they show the old domain, with old prices and a phone number that no longer works.
Unwanted mirrors
Some mirrors aren't yours. Scrapers copy whole sites to show ads next to the content, sometimes at addresses that look close to yours. If a copy outranks you, you can ask its host to take it down, or report it to Google as a copyright issue.
Mirrors and AI search
An AI platform that searches the web can find a mirror as easily as your site. If it reads the copy, the answer may cite the copy's address instead of yours, or repeat old details from a mirror that stopped being updated.
In AnswerOrbit, Sources sorts every page the answers used by who owns it. If you see a copy of your own content listed as someone else's site, you've found a mirror. If it's one of yours, add the domain to your names in Settings so we count it as you.