Grey (or gray) literature is …
“information produced on all levels of government, academics, business and industry in electronic and print formats… i.e, where publishing is not the primary activity of the producing body."
(International Conference on Grey Literature, Luxembourg,1997 – Expanded in New York, 2004)
Source: GreyNet: grey literature network service. Amsterdam: GreyNet; 2008.
Therefore, grey literature could be:
• Non-commercial material
• In-house, vertical files
• Information on the deep Web
• “Hard to find”
To see more specialized and authoritative sources of grey literature, please refer to the "Special Topics" Tab on THIS library guide.