Whenever we talk about open source we only talk about big coding projects with contributions from aound the world. An openly available source code and all. I was wondering going with the spirit or the philosophy of open source aren't freely available books also part of open source. I also read somewhere that they are but I don't know if that was a reliable source. So, please clarify.
My understanding is that technically any code belongs to the author. Open Source basically means that others are allowed to modify the source code while giving acknowledgement to any previous authors of the code. Until the author gives such permission no one else has the right to copy his/her work. The size of the project is immaterial.
I want to know if freely available books are considered as a contribution to open source?
Open source does not only apply to programming. If you consider "source" as meaning any kind of blueprints, models, design specifications, or typesetting (word document or latex files), basically anything that is the basis for making something whether it is a software, a book, or a physical product of some kind, then the open source term can apply to it, if it meets the concept of being "open". Without getting into licensing politics, the essential elements of being "open" is that it is widely available and can be modified by anyone (and maybe contributed to by anyone).
In that sense, Wikipedia is an open source encyclopedia. Anyone can access the typesetting source of wikipedia pages and can contribute to it. Any wikipedia-style page qualifies in a similar way.
And if you stretch things a bit (but not that much), you could say that standards (like ISO or ANSI standards) are essentially open source projects, and in fact, many of them are prefixed with "Open" for exactly that reason, like "OpenGL". Standards are available to all, can be followed by anyone wishing to do so, and can generally be contributed to openly (through committee participation or proposals given to the committee). Most standards work this way.
aren't freely available books also part of open source.
It is not sufficient that the book is freely available to be considered "open source". In fact, the price tag is not a factor at all. As the saying goes, open source is free as in "freedom" not as in "free beer". If you write a book and decide to just give it out free of cost, that doesn't make it an open-source project. If you open it up for contributions from others, sort of in the way wikipedia does it or maybe in a more controlled manner (e.g., by approving people's contributions before letting them in), then you are talking about an open source project. I don't know of any actual books that are written like that on an on-going basis.
The basic test to know if something is open-source or not is simply to ask "could I take this thing, make some modifications to it, and make a new thing?". In legal speak, the things are called "works", and the new thing that was created by a modification to the original thing is called a "derivative works". So, for example, if you have a free book that you can get as a pdf, could you take that book, add a paragraph or chapter to it and make a new book with it? The answer is usually "no" (although, if you really want, you could probably contact the author and propose your modifications to him, but that isn't really "free"). So, both legally and in practice, what really matters is how "open" it is, not so much what kind of work it is (it just happens to be much more common for software, because it's a lot easier to share and re-create (re-compile)).