This article is from the CD-Recordable FAQ, by Andy McFadden (firstname.lastname@example.org) with numerous contributions by others.
HighMAT stands for High Performance Media Access Technology. Co-developed
and supported by Microsoft and Matsushita (Panasonic), it was first announced
in October 2002. HighMAT defines formats for storing digital media (music,
photos, videos) on CD-R/RW discs and (eventually) writable DVD formats.
While many DVD players now recognize MP3 and JPG files on ISO-9660 discs,
they don't all do things the same way, and may not support all formats.
A HighMAT-compliant player would be able to handle all files on discs
created in HighMAT format. The end result is that you would be able to
record a disc full of music or pictures in HighMAT format and send it to
anybody with a HighMAT player and know that it will work.
This format has not yet been adopted by most consumer electronics companies,
so it remains to be seen whether this will become a significant feature.
For details, see http://www.highmat.com/.