In order to better understand what is meant by the term "Libre Documentation," we need to explore what Libre means. To better illustrate this, let us look at the definition of Libre from a "Libre Software" standpoint. Libre Software is also known as "Free Software," but this is usually where the definition becomes skewed.
What most people define as free software is not necessarily really free because it may be restricted, in that the user may not have access to the source code. The term "free" with respect to software and documentation is often misinterpreted to mean "gratis", or free of cost.
In an open source community, this is not an accurate representation of free software, so instead, the term Libre is used. In Spanish and French, Libre, as opposed to Gratis, indicates liberty or freedom rather than price. In order for a software application to be considered Libre, these following conditions need to be met:
The user has the liberty or freedom to run the program, for any purpose.
The user has the liberty to understand how the program works and adapt it to his or her needs. This means the source code of the program is available to view and edit.
The user has the liberty to make improvements to the software and release those improvements to the public, for the benefit of the entire community.
The user has the liberty to redistribute copies or modified copies of the program.
Likewise, for Libre Documentation, the same definition applies. Libre Documentation is documentation that one can copy or enhance as long as these inherent freedoms are met. In addition, for documentation to be classified as Libre, we need to consider the following:
Documents should come with a human readable and editable source (html, txt, xml are ok, pdf dvi or ps are not, since they cannot be edited without proprietary software).
They should be copylefted so that new versions can be created from the exisiting base, just like a software fork.
They may be sold, or given away - this freedom should not be impaired by additional requirements (such as 'no commercial printing allowed').