The Jargon File (version 4.4.7, 29 Dec 2003):

link rot
 n.

    The natural decay of web links as the sites they're connected to change or
    die. Compare bit rot.


The Free On-line Dictionary of Computing (30 December 2018):

link rot

    The process by which links on a web page
   became unusable as the pages they point to change location or
   are removed.

   (1997-03-29)