A really good definition of what a white paper is and isn't can be found on the Purdue OWL's website.
Here is an example:
Originally, the term white paper was used as shorthand to refer to an official government report, indicating that the document is authoritative and informative in nature. Writers typically use this genre when they argue a specific position or propose a solution to a problem, addressing the audience outside of their organization. Today, white papers have become popular marketing tools for corporations especially on the Internet since many potential customers search for information on the Web. Corporations use white papers to sell information or new products as solutions that would serve their customers' needs.
Typically, the purpose of a white paper is to advocate that a certain position is the best way to go or that a certain solution is best for a particular problem. When it is used for commercial purposes, it could influence the decision-making processes of current and prospective customers.
Read more at this link: https://owl.english.purdue.edu/owl/owlprint/546/.
This paper is written in the style of a white paper and it is about how to write a white paper: http://coe.winthrop.edu/educ651/readings/HowTo_WhitePaper.pdf
This is an example of a white paper on public health advocacy: http://gatesinstitute.org/sites/default/files/White%20Paper%20on%20Advocacy_100614.pdf
A white paper on Bitcoin: https://bitcoin.org/bitcoin.pdf