Dead links are links pointing to a URL that is no longer reachable, usually returning status code 404. Internal dead links that lead users and crawlers into a dead end are especially problematic.
(broken links) are links pointing to a URL that is no longer reachable, usually returning . They can be internal (within your own site) or external (from other sites to yours).
Especially problematic are internal dead links, because your own site leads users and crawlers into a dead end. Consequences include:
users are more likely to bounce,
signals are interrupted,
crawlers waste time on non-existent URLs.
Internal dead links should be fixed directly at the source rather than permanently masking them with a . External dead links are not always your problem; they become relevant mainly when the target URL had backlinks or traffic. In that case a to a suitable page is often advisable.