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

frobnitz
 /frob'nits/, pl., frobnitzem, /frob?nit?zm/, frob?ni, /frob'?ni:/,
    n.

    [TMRC] An unspecified physical object, a widget. Also refers to electronic
    black boxes. This rare form is usually abbreviated to frotz, or more
    commonly to frob. Also used are frobnule (/frob'n[y]ool/) and frobule (/
    frob?yool/). Starting perhaps in 1979, frobozz /fr@-boz'/ (plural:
    frobbotzim /fr@-bot?zm/) has also become very popular, largely through its
    exposure as a name via Zork. These variants can also be applied to
    nonphysical objects, such as data structures. For related amusement, see
    the Encyclopedia Frobozzica.

    Pete Samson, compiler of the original TMRC lexicon, adds, ?Under the TMRC
    [railroad] layout were many storage boxes, managed (in 1958) by David R.
    Sawyer. Several had fanciful designations written on them, such as
    ?Frobnitz Coil Oil?. Perhaps DRS intended Frobnitz to be a proper name, but
    the name was quickly taken for the thing?. This was almost certainly the
    origin of the term.


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

frobnitz

   /frob'nits/, plural "frobnitzem" /frob'nit-zm/ or "frobni"
   /frob'ni:/ (TMRC) An unspecified physical object, a widget.
   Also refers to electronic black boxes.  This rare form is
   usually abbreviated to "frotz", or more commonly to frob.
   Also used are "frobnule" (/frob'n[y]ool/) and "frobule"
   (/frob'yool/).  Starting perhaps in 1979, "frobozz" /fr*-boz'/
   (plural: "frobbotzim" /fr*-bot'zm/) has also become very
   popular, largely through its exposure as a name via Zork.
   These variants can also be applied to nonphysical objects,
   such as data structures.

   Pete Samson, compiler of the original TMRC lexicon, adds,q
   "Under the TMRC (railway) layout were many storage boxes,
   managed (in 1958) by David R. Sawyer.  Several had fanciful
   designations written on them, such as "Frobnitz Coil Oil".
   Perhaps DRS intended Frobnitz to be a proper name, but the
   name was quickly taken for the thing".  This was almost
   certainly the origin of the term.

   [Jargon File]

   (1994-12-16)