DuckCorp Dico

Found one definition

1.                 From The Free On-line Dictionary of Computing (19 January 2023):
                   
   
   
                   
                     
   Directory User Agent
   DUA
      (DUA) The software that accesses the X.500 Directory Service
      on behalf of the directory user.  The directory user may be a
      person or another software element.
      (1994-12-07)