Source : Free On-Line Dictionary of Computing

Interchange File Format
     
         (IFF, full name "EA IFF 1985") A generic file
        format published by {Electronic Arts} as an open standard.
        IFF is {chunk}-based and hierarchical so files can include
        other files.  It is easily extensible and an all round Good
        Idea.
     
        An IFF file starts with one of the following "group IDs":
        'FORM', 'LIST' or 'CAT '.  This is followed by an unsigned
        32-bit number of bytes in the remainder of the file.  Then
        comes an ID that indicates which type of IFF file this is.
        The main image type is {ILBM}, {audio} is either {AIFF} or
        {8SVX}, animations are {ANIM} etc.  An IFF file will probably
        have a {filename extension} related to this file type stored
        in the file.  The rest of the file is divided into {chunks}
        each of which also has a four-byte header and byte count.
     
        {Microsoft} {WAV} and {AVI} are all based around an almost
        identical scheme to IFF called {RIFF}.  The main difference is
        that, in RIFF files, numbers are little-endian as on {Intel}
        processors, whereas in IFF files they are big-endian, as on
        the {Motorola 68000} processors in the {Amiga} where IFF files
        were first used.
     
        (1997-07-23)