If I want something I have written release as open source, for instance a novel, is that possible? A novel does not have a source, the work itself is all that is needed to recreate the work. In cases of software I need the source code to create a changed version of the software, but in case of a novel all I need is the novel itself? So does the written text works as it's own source? Or are written text impossible to open source?
Novels, unlike software, don't have the large transformation between source code and binary that is usually the case with software. You can study and "tinker" with novels, but you cannot do the same (without great difficulty) with software without source code. Source code is important for software since it is a prerequisite for modification and sharing derivations. Therefore terms like "source code" are mostly irrelevant for novels, or things like visual art and documentation.
It is for this reason that, although you can apply software licenses to them, there are much better options. This is a big reason why the Creative Commons licenses were created; they, unlike software licenses, contain no mention of "source code" and are designed for creative works in general. GFDL may also be a suitable free license for such works.
When referring to such licenses, it may be less appropriate to refer to them as "free software" or "open source". Instead, people usually refer to these as "free culture". Even though there is no source code, the goals and ethoses have large overlaps, and focus on user freedoms such as the freedom to use for any purpose, the freedom to redistribute, and the freedom to share your modifications. If you compare this to FSF's definition of free software, this is almost the same with the exception of freedom 1 which is inapplicable. Those licenses that do not grant these freedoms are "not free culture licenses", or just "non-free" for short. For example, CC-BY-NC is "not approved for free cultural works" because it restricts commercial use.
Novels and other written works do have source code: it's the "preferred form for modification", so basically the files you need if you want to edit the "work", whatever it is. If you write your novel in LibreOffice, it's the
.odt file, plus any external files you may need (images, diagrams etc.). If you write it in LaTeX, it's the
.tex file, plus any external files required. Don't forget any files you may use to prepare the final output (the cover, etc.). For images, ideally you'd keep the
.xcf files for example if you're using the Gimp, as well as the PNGs or JPEGs you use in the document.
If you work directly on paper (handwriting or using a typewriter or whatever), then the preferred form for modification is the manuscript because that's all there is. You can still use a free / open source license on the text though; it's just that the effort required is greater... (This is pretty much the same reasoning as allowing JPEGs of photos as the preferred form for modification, rather than everything that was photographed!)
So yes, you can open source written text.