Source : Free On-Line Dictionary of Computing

command line option
     
         (Or "option", "flag", "switch", "option switch") An
        argument to a command that modifies its function rather than
        providing data.  Options generally start with "-" in {Unix} or
        "/" in {MS-DOS}.  This is usually followed by a single letter
        or occasionally a digit.
     
        Some commands require each option to be a separate argument,
        introduced by a new "-" or "/", others allow multiple option
        letters to be concatenated into a single argument with a
        single "-" or "/", e.g. "ls -al".  A few Unix commands
        (e.g. {ar}, {tar}) allow the "-" to be omitted.  Some options
        may or must be followed by a value, e.g. "cc prog.c -o prog",
        sometimes with and sometimes without an intervening space.
     
        {getopt} and {getopts} are commands for parsing command line
        options.  There is also a {C} library routine called getopt
        for the same purpose.
     
        (1996-12-11)