Source : Free On-Line Dictionary of Computing

pathname separator
     
         The character used to separate elements of a
        {path} or {pathname}.  Under {Unix} and {POSIX.1} compliant
        systems the pathname separator is the (forward) {slash}, in
        {MS-DOS} {backslash} serves the same purpose.  For obvious
        reasons the no directory or file name can contain this
        character.
     
        (1996-11-21)