Orphan page

An orphan page is defined by exactly one thing: no other page on your site links to it. That does not make it invisible. It can still be found through an external backlink, your XML sitemap, an RSS feed, a campaign URL in analytics, or plain search results. What it lacks is a seat in your internal link graph, and crawlers move by following links, so it gets discovered late or never, gets recrawled rarely, and inherits no authority from the rest of the site. A genuinely good page can end up ranking like it does not exist.

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.