Is it "gray" or "grey" literature? In America, the spelling is grAy, while in England the spelling is grEy. [From http://www.greyorgray.com/].
Search tip: As both spellings are acceptable, use the following search string: (gray OR grey) literature
Gray (or grey) Literature generally refers to multiple document types produced on all levels of government, academics, business, and organization in electronic and print formats not controlled by commercial publishing, i.e., where publishing is not the primary activity of the producing body.
A few examples are newsletters, technical notes, working papers, white papers, patents, reports, conference proceedings, doctoral theses/dissertations.
To learn more about the topic, consult the website of GreyNet International (http://www.greynet.org/).