The Free On-line Dictionary of Computing (30 December 2018):

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)