This is literature which typically falls outside the realm of mainstream/commercial publishing. GreyNet defines gray literature as: "...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."
Different types of gray literature include:
Want to learn more about Gray Literature? Check out these information sources:
ProQuest Dissertations & Theses Global -- The most most comprehensive collection of full text dissertations and theses from 1743 to the present, expanded to provide international dissertations.
PsycEXTRA -- a unique database that combines bibliographic records with full-text professional and lay-audience literature such as legal testimony and amicus briefs, reports, conference materials, popular magazines, fact sheets, grants, and web materials. It is the premier resource for information and data for cutting-edge research and practice in the behavioral and social sciences and an archive of gray literature documenting psychology's development.
ClinicalTrials.gov -- a registry and results database of publicly and privately supported clinical studies of human participants conducted around the world.
EThOS -- e-theses online service from the British Library.
GreySource Index -- provides examples of grey literature to the average net-user and in so doing profiles organizations responsible for its production and/or processing. Only web-based resources that explicitly refer to the term grey literature (or its equivalent in any language) are listed. GreySource identifies the hyperlink directly embedded in a resource, thus allowing immediate and virtual exposure to grey literature.
HSRProj -- From the U.S. National Library of Medicine. Information about ongoing health services research and public health projects. HSRProj provides information about research-in-progress before results are available in a published format.
NTIS.gov -- The National Technical Information Service, the nation's top resource for government reports and information. Serves as the largest central resource for government-funded scientific, technical, engineering, and business related information available today. For more than 60 years NTIS has assured businesses, universities, and the public timely access to approximately 3 million publications covering over 350 subject areas.
OpenDOAR -- an authoritative directory of academic open access repositories