Debian is Free Software....sort of
It even has its own Guide in this regard; the Debian Free Software Guide (DFSG).
Free software is a matter of liberty, not price. To understand the concept, you should think of “free” as in “free speech”, not as in “free beer”.
The Free Software Foundation explores this concept in depth:
https://www.gnu.org/philosophy/free-sw.html
The FSF however, does not consider Debian to be free software:
"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."
This is a fairly strict implementation of its charter if you ask me. It reminds me, mutatis mutandis, of the antitrust action that was taken against Microsoft in the 90's (United States v. Microsoft Corp). An issue at hand then was whether Internet Explorer was a part of Windows, or was it a separate product.
For Instance, there is some software, that is often necessary for some users that is NOT free software, like Adobe Flash Player.
When users install this on their Debian machines, does it become a part of the Operating System, thus rendering it Non Free, or is it separate program?
For Installation purposes, Debian maintains three archive areas: 'main' 'contrib' and 'non-free'.
'main' is where the actual distribution packages live, none of the packages here depend on any other packages to work.
'contrib' is where supplemental software packages live that require software outside of the distributon to function. These packages must comply with the DFSG.
'non-free' is where other supplemental software packages live. They do not comply with the DFSG.
Debian maintains its sources in: /etc/apt/sources.list
When Debian is first installed, this file contains something like this:
#
# deb cdrom:[Debian GNU/Linux 8.1.0 _Jessie_ - Official amd64 NETINST Binary-1 20150606-14:16]/ jessie main
#deb cdrom:[Debian GNU/Linux 8.1.0 _Jessie_ - Official amd64 NETINST Binary-1 20150606-14:16]/ jessie main
deb http://ftp.ie.debian.org/debian/ jessie main
deb-src http://ftp.ie.debian.org/debian/ jessie main
deb http://security.debian.org/ jessie/updates main
deb-src http://security.debian.org/ jessie/updates main
# jessie-updates, previously known as 'volatile'
deb http://ftp.ie.debian.org/debian/ jessie-updates main
deb-src http://ftp.ie.debian.org/debian/ jessie-updates main
If you do:
# apt-get install flashplugin-nonfree
You'll get an error saying that the package requested has no installation candidate.
So you have to update the sources.list to include the 'non-free' and 'contrib' archive areas:
deb http://ftp.ie.debian.org/debian/ jessie main contrib non-free
Then do:
#apt-get update
and once again:
# apt-get install flashplugin-nonfree