'Open Source' refers to systems and software products that are freely available online to all users and for which the source code is freely available for use, modification, and re-distribution.
'Public Availability' describes webpages and information items that are freely available to anyone with internet access.
'Open Access' is a term used to describe scholarly work that has been made freely available to all online.
"That which is produced on all levels of government, academics, business and industry in print and electronic formats, but which is not controlled by commercial publishers." - The Fourth International Conference on Grey Literature, October 1999
Grey literature is an umbrella term which covers many types of information sources and products. Grey literature is produced by organizations whose primary function is NOT publishing. Grey literature includes reports from governmental agencies, professional organizations, advocacy organizations, and think tanks.
White Papers fall under the grey literature umbrella and are a type of authoritative reporting that typically cover governmental, social, or consumer issues. White papers are prepared by governmental agencies, professional organizations, public policy and research organizations, and commercial enterprises. By definition, they are based upon an exhaustive research process and frequently address new, controversial or developing trends, programs or products.
"Think tanks are organizations that have significant autonomy from governmental interests and that synthesize, create, or disseminate information, ideas, or advice to the public, policymakers, other organizations, and the press."
Anderson, G. L. & Herr, K.G. (Eds) (2007). Think Tanks. In Encyclopedia of Activism and Social Justice. (Vol. 3, pp. 1369-1372). Thousand Oaks, CA: SAGE Reference. Retrieved here.
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