[Izkata]

> one that customarily means "pass the rest of arguments on to a subprocess".

It's convenient for passing options and args to a subprocess, but it customarily means "don't interpret anything following this as a short or long option, just as a positional argument". For example:

  touch -f     # error
  touch -- -f  # creates a file named "-f"
  rm *         # oh crap we just passed "rm -f" a bunch of files
  rm -- *      # don't treat that "-f" as an option, just delete the file named "-f"