When Debian developers and users speak of “free software”, they refer to freedom rather than price. Debian is free in this sense: you are free to modify and redistribute it, and will always have access to the source code for this purpose. The Debian Free Software Guidelines describe in more details exactly what is meant by “free”. The Free Software Foundation, originator of the GNU project, is another source of information. You can find a more detailed discussion of free software on the Debian web site.
Free software is sometimes called Open Source (R) software — Open Source is a certification mark. Since Open Source (R) is trademarked, only truly free software can call itself Open Source (R). You may encounter vendors who try to mislead you by claiming their software is “free”, while in reality it has significant strings attached. The Open Source (R) trademark gives you some assurance that the software really is free software. ‘Open Source software’ is occasionally abbreviated ‘OSS’.
You may be wondering: why would people spend hours of their own time to write software, carefully package it, and then give it all away? The answers are as varied as the people who contribute.
Many believe in sharing information and having the freedom to cooperate with one another, and feel that free software encourages this. There’s a long tradition starting in the 1950s upholding these values, sometimes called the Hacker Ethic. (You can read more about it in Steven Levy’s enjoyable book, Hackers: Heroes of the Computer Revolution.)
Others want to learn more about computers. More and more people are looking for ways to avoid the inflated price of commercial software. A growing crowd contribute as a thank you for all the great free software they’ve received from others.
Many in academia create free software to help get the results of their research into wider use. Businesses help maintain free software so they can have a say in how it develops — there’s no quicker way to get a new feature than to implement it yourself or hire a consultant to do so! Business is also interested in greater reliability and the ability to choose between support vendors.
Still others see free software as a social good, democratizing access to information and preventing excessive centralization of the world’s information infrastructure. Of course, a lot of us just find it great fun.
Debian is so committed to free software that we thought it would be useful if it was formalized in a document of some sort. Our Social Contract promises that Debian will always be 100% free software. When you download a package from the Debian main distribution, you can be sure it meets our Free Software Guidelines.
Although Debian believes in free software, there are cases where people want or need to put proprietary software on their machine. Whenever possible Debian will support this; though proprietary software is not included in the main distribution, it is sometimes available on the ftp site in the non-free directory, and there are a growing number of packages whose sole job is to install proprietary software we are not allowed to distribute ourselves.
It is important to distinguish commercial software from proprietary software. Proprietary software is non-free software, while commercial software is software sold for money. Debian permits commercial software to be a part of the main distribution, but not proprietary software. Remember that the phrase “free software” does not refer to price; it is quite possible to sell free software. For more clarification of the terminology, see http://www.opensource.org or http://www.fsf.org/philosophy/categories.html.
Sources: Debian Manual Book