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As a consequence, it offers the possibility to see how it works, its precise design. This allows specialists, for example university researchers, to study and validate it. On principles of confidentiality, or other respect for privacy, which will have been implemented. Similarly with various issues of technical quality in general and security in particular. Its openness is therefore an important technical guarantee. This is why these freedoms offered do not only concern computer specialists, but all users.
The author of free software starts from the principle that it is good to know how it works so that others can learn from it and, together, participate in the improvement of the program or other similar programs.
Free software uses open formats, i.e. ways of saving files so that other programs can use or change them easily. For example, HTML, the format of web pages, is an open format, allowing many different people to produce them and different browsers to read them easily all over the web.
On the other hand, we have all encountered problems with video files that are difficult to read, or that require a special player. These video formats are said to be closed.
Closed formats correspond to closed programs, non-free software. They are often referred to as proprietary or private software. If you are sent a document (video, text, graphics, presentation or other) in a closed format, you usually need the closed program that goes with it. Usually, this program is paid for.
These programs are therefore closed, and even opaque. This means that users cannot know how they work, let alone (have) them corrected or adapted to their needs. So we never buy these programs, but just a right to use, usually limited to one person. And we are even forbidden to try to understand how our files produced with these programs are constructed, and which contain our work (our video, our presentation, our text, etc.). If in five years' time the program has been abandoned, our files may no longer be able to be displayed anywhere.
Free software is therefore a program that guarantees you four freedoms:
to use this program for any purpose without restriction,
study how it works, modify it as you wish,
make copies and distribute them to whomever you want,
to circulate modified versions, provided that the modifications made are clearly specified and that the result is shared under the same conditions (these four freedoms).
See also: the GNU Project.