Orphan page
A live page no other page on your site links to, reachable only by typing the URL. Crawlers walk links, so it stays invisible.
See it
What it is
Crawlers move by following links. A page with zero inbound internal links sits outside that graph: it gets discovered late or never, gets recrawled rarely, and inherits no authority from the rest of the site, so it ranks like it does not exist even when it is genuinely good.
How pages get orphaned: a campaign landing page nobody added to the nav, old URLs left live after a redesign, CMS items whose category page was deleted, paginated or filtered URLs that fell off the last page, and links that only appear inside a JavaScript menu the crawler never executes. To find them, crawl the site with something like Screaming Frog or Sitebulb and diff the crawl graph against your XML sitemap, your server logs, and the URL list in Search Console. Anything present there but absent from the crawl is an orphan.
Gotcha: adding the URL to your sitemap is not a fix. A sitemap is a hint about existence; internal links are the vote about importance, and an orphan can be perfectly indexed and still rank nowhere. Link it from a relevant hub page plus two or three related articles, or decide it should not exist and redirect it. Deliberate orphans (thank-you pages, gated offers) are fine, just mark them noindex so nobody grades them.
Ask AI for it
Find the orphan pages on this site and fix them. Crawl it starting from the homepage, build the internal link graph, then diff that set against the URLs in the XML sitemap and any analytics or Search Console export I give you. Output a table of URLs with zero inbound internal links, their click depth if reachable at all, and their indexed status. For each orphan, recommend one of: link it from a named hub page and two related posts, 301 it to the closest equivalent, or noindex it as intentionally unlisted.