Source : Free On-Line Dictionary of Computing

MZ
     
         The file signature of an {MS-DOS}
        executable (.{EXE}) file (0x4d 5a), always the first two
        {bytes} of the file.  It was reportedly invented by, and named
        after, a {Microsoft} programmer, Mark Zbikowski.
       
        In {Unix} systems, the string MZ is the {magic number} that
        identifies an MS-DOS EXE file.
     
        (2003-06-10)

mz
     
         The {country code} for Mozambique.
     
        (1999-01-27)