broken link

Link rot (also called link death, link breaking, or reference rot) is the phenomenon of hyperlinks tending over time to cease to point to their originally targeted file, web page, or server due to that resource being relocated or becoming permanently unavailable. A link that no longer points to its target, often called a broken or dead link, is a specific form of dangling pointer.
The rate of link rot is a subject of study and research due to its significance to the internet's ability to preserve information. Estimates of that rate vary dramatically between studies.

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