The contents of TeX Live release are also available as large compressed tar files on tug.org. They are primarily for the benefit of distro maintainers, since tar files are easier to work with than ISO images. They are not useful as a direct installation source.
The tar files include: texmf (the texmf trees), source (the TL-specific sources), bin (the binaries distributed with TL), and extra (miscellaneous other files).
Please don't download these from tug.org unless you know you need them.
Information about downloading TeX Live as an ISO image is available separately, as well as other ways to acquire TeX Live.