There are two major terms connected to software you can freely use, study, share and improve: Free Software and Open Source. Based on them you can also find different combinations and translations like FOSS, Libre Software, FLOSS and so on. So why do people use these terms, and how are they different from one another?
Historically, Free Software was the first term, created 1986 together with the Free Software definition. In 1997 Debian, a project aiming to create a completely free and community based GNU/Linux distribution, developed the Debian Free Software Guidelines (DFSG) as a check-list whether a program can be included in the distribution or not. One year later, the Open Source Initiative (OSI) was set up as a marketing campaign for Free Software. It introduced the Open Source definition by copying the DFSG and replacing "Free Software" with "Open Source". According to a public statement by Bruce Perens, one of the founders of the OSI and author of the DFSG and Open Source Definition, the Open Source term was intended as a synonym for Free Software. Perens eventually decided to return to the roots of the movement and to speak about Free Software again. Thanks to their shared roots, both Open Source and Free Software describe the complete set and the whole range of software licenses that give users the right to use, study, share and improve the software1.
In the course of time people came up with additional labels for the same set of software. Today terms such as Libre Software, FOSS (Free and Open Source Software) or FLOSS (Free, Libre and Open Source Software) are often used to describe Free Software. In some cases people also use terms like "organic software" or "ethical software". Often the motivation for these terms is to stay out of the terminology debate and to avoid confusion through words like "open" or "free". These terms tend to cause confusion, because they virtually invite people to look for differences between the terms where actually no differences exists, regarding the software they describe.
This short summary of the historical origin of the different terms should show that at the end all of them have the same root and refer to the same set of software.
The Free Software movement is a large and diverse community. People have different interests in Free Software and different reasons to participate. But these differences don't necessarily connect with the terms they use. A lot of people use the term Open Source even while highlighting the social and political dimension of Free Software while on the other hand there are people in our community who prefer the term Free Software but concentrate more on the practical benefits. Whether someone says Open Source or Free Software isn't necessarily an indication of their motivation.
Beside individuals there are also many well known organisations in the Free Software ecosystem. Many of them play an important role and emphasize different aspects of Free Software. For example, some organisations focus on the technical direction of Free Software projects, some on legal aspects, some on political, social and ethical aspects and some focus on license evaluation. These organisations typically have decided to use one or another term and stick to it. But this should not lead to the conclusion that the term they use is the critical factor regarding their motivations. The critical factor are the people driving the organisation and the goals of the organisation as such. The practical experience with different organisations and people in the community shows that the line can't be drawn along the language they use.
This diversity is good, as it shows that Free Software provides many advantages in many different areas of our life. But we should not divide our community just by the term someone prefers. No matter what term someone uses and what their initial motivation is, in the end they works on the same set of software and on the enhancement of software freedom and any other aspect of Free Software.
There are three widely recognized entities in the Free Software movement that regularly evaluate licenses: The Free Software Foundation, the Debian project and the Open Source Initiative. When asked whether a particular license gives software users the freedom to use, study, share and improve the program, they almost always come to the same conclusions.
Looking at Free Software licenses there are two main categories, protective or Copyleft licenses and non-protective licenses. While Copyleft licenses are designed to protect the rights to use, study, share and improve the software non-protective licenses allow to distribute the software without those rights. Sometimes people think that the terms Free Software and Open Source are used to distinguish between Copyleft and non-Copyleft licenses. The lists of Free Software licenses by Debian, the FSF and the OSI show that both protective and non-protective licenses comply with the Free Software definition and the Open Source definition. This means that neither the terms Open Source and Free Software nor the different definitions are suitable to distinguish between Copyleft and non-Copyleft licenses.
Protective licenses and non-protective licenses are sub-classes of Free Software licenses recognized by the Open Source Initiative and the FSF. Copyleft or non-Copyleft is not a criteria suitable to distinguish between Open Source and Free Software, both terms describe the same set of software.
The way a program is developed can be a crucial factor in its success or failure. But whether a program is written in an open, participatory process or behind closed doors doesn't tell us whether it is non-free or Free Software.
When looking at software we have to distinguish between the software model and the development model. While the software model describes the attributes of the software (e.g. free or proprietary) the development model describes different ways to develop software. As discussed in detail in "What makes a Free Software company?" the different software development models are defined independently of the software model and work for both Free Software and proprietary software. Models that leverage the advantage of an open and collaborative community can show their full strength in combination with the Free Software model. However this does not mean that any program developed in an open, collaborative development process is Free Software. There are Free Software projects developed by a single person or a company with little or no outside input. On the other hand developers of proprietary software have adapted collaborative development models to fit into their software model, e.g. SAP with its partnership program.
If all these terms describe the same set of programs, why do we at FSFE insist on using the term Free Software?
Free Software is all about your freedom. That's a message we want to get across loud and clear. Language is important because it frames how people think about a subject. The different terms focus on different aspects, even if they describe the same software. Freedom is a core value of Free Software, and our language reflects this. This makes Free Software the right choice for FSFE and we invite you to follow us.