Wikipedia:1.5 sources

1.5 sources is a term that relates to the use of sources that cannot strictly be categorised as being either primary sources or secondary sources, mostly in fiction-related articles: interviews with key people, DVD commentary, etc.

It is often a matter of personal preference whether one sees such a source as a primary source that cannot provide any significant real-world perspective or whether one sees it as more of an independent, secondary source which can and should be used to add context and perspective.

For such situations, 1.5 sources can serve as a neutral term to start negotiations from a middle-ground, namely that such source-related issues have to be decided on a case-by-case basis, and how an individual source is used is more important than categorical judgements.