From Xavier Leroy, one of the lead Ocaml developers [1]:

    I think I'm the one who coined the name "C--" to refer to a low-level,
    weakly-typed intermediate code with operations corresponding roughly
    to machine instructions, and minimal support for exact garbage
    collection and exceptions.  See my POPL 1992 paper describing the
    experimental Gallium compiler.  Such an intermediate code is still in
    use in the ocamlopt compiler.

    I had many interesting discussions with Simon PJ and Norman Ramsey
    when they started to design their intermediate language.  Simon liked
    the name "C--" and kindly asked permission to re-use the name.

    However, C-- is more general than the intermediate code used by
    ocamlopt, since it is designed to accommodate the needs of many source
    languages, and present a clean, abstract interface to the GC and
    run-time system.  The ocamlopt intermediate code is somewhat
    specialized for the needs of Caml and for the particular GC we use.