Glossary:
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.
Link Rot results in 404 "not found" error messages. Links that do not work are referred to as Dead Links.