Here's what gnu.org/distros says:
> Debian's Social Contract states the goal of making Debian entirely free
> software, and Debian conscientiously keeps nonfree software out of the
> official Debian system. However, Debian also provides a repository of
> nonfree software. According to the project, this software is “not part of
> the Debian system,” but the repository is hosted on many of the project's
> main servers, and people can readily learn about these nonfree packages by
> browsing Debian's online package database.
>
> There is also a “contrib” repository; its packages are free, but some
of
> them exist to load separately distributed proprietary programs. This too is
> not thoroughly separated from the main Debian distribution.
>
> Previous releases of Debian included nonfree blobs with Linux, the kernel.
> With the release of Debian 6.0 (“squeeze”) in February 2011, these
blobs
> have been moved out of the main distribution to separate packages in the
> nonfree repository. However, the problem partly remains: the installer in
> some cases recommends these nonfree firmware files for the peripherals on
> the machine.
