A broken link is a hyperlink that leads nowhere useful — the destination returns a 404, the server is unreachable, or the URL was mistyped. Visitors hit a dead end, and crawlers spend budget requesting pages that no longer resolve, which is why broken links quietly erode both experience and rankings.
Most broken links trace back to ordinary site changes: a page is deleted without a redirect, a URL slug is edited, a product is discontinued, or an external site you linked to reorganises and drops the target. A single typo in an href does it too. On large sites these accumulate faster than teams realise, because one removed page can be linked from dozens of others.
An online store discontinues a popular jacket and deletes the product page. Nothing redirects it, yet 180 internal links and a handful of external blog mentions still point there. Every click and crawl lands on a 404. After a crawl audit surfaces the dead URL, the team 301-redirects it to the closest in-stock alternative and updates the highest-value internal links directly. Crawl errors drop to zero, the inherited link value flows to a live page, and shoppers stop bouncing off an error screen.
A scheduled SEO audit catches these before they pile up. Broken links are also called defective links, and keeping your internal linking tidy prevents most of them.