Glossary:
Dead Links
A Dead Link is sometimes called a broken link or dangling link. These are links on a web page that point to a resource that is not available. Dead links result in 404 "not found" error messages.
One of the most common causes of dead links is Link Rot. Link Rot is the slow occurrence of links that become broken to the pages they link back to. This happens because websites change content, move or disappear. Link Rot happens mainly on links to external resources (web pages on other sites) as the web owner of one site has no control of the web pages or content on another website.