DuckCorp Dico

Found one definition

1.                 From The Free On-line Dictionary of Computing (19 January 2023):
                   
   
   
                   
                     
   DED
      Dark-Emitting Diode (that is, a burned-out LED).  Compare
      SED, LER, write-only memory.  In the early 1970s both
      Signetics and Texas instruments released DED spec sheets as
      AFJs (suggested uses included "as a power-off indicator").
      [Jargon File]