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

system software

    Any software required to support the
   production or execution of application programs but which is
   not specific to any particular application.

   System software typically includes an operating system to
   control the execution of other programs; user environment
   software such as a command-line interpreter, window
   system, desktop; development tools for building other
   programs such as assemblers, compilers, linkers,
   libraries, interpreters, cross-reference generators,
   version control, make; debugging, profiling and
   monitoring tools; utility programs, e.g. for sorting,
   printing, and editting.

   Different people would classify some or all of the above as
   part of the operating system while others might say the
   operating system was just the kernel.  Some might say system
   software includes utility programs like sort.

   (2007-02-02)