All packages that are included in the official Debian distribution are free according to the Debian Free Software Guidelines. This assures free use and redistribution of the packages and their complete source code. The official Debian distribution is what is contained in the main section of the Debian archive.
This is just a quick tip. If you are getting this error message:
E: Unable to parse package file /var/lib/apt/extended_states (1)
Then just execute this in command line (terminal):
mv /var/lib/apt/extended_states /var/lib/apt/extended_states_tmp
You are done.