Grey literature has been defined as:
"Information produced on all levels of government, academics, business and industry in electronic and print formats not controlled by commercial publishing, i.e. where publishing is not the primary activity of the producing body"
-ICGL Luxembourg definition, 1997-expanded in New York, 2004
Grey literature can be hard to find or irretrievable for a number of reasons because it is:
- not widely disseminated - e.g. conference proceedings, institutional working papers, theses
- often not archived
- available only in obsolete formats
- It is part of the Invisible web
A lot of grey literature is available on what is called the Invisible, Hidden or Deep Web.
These are terms used to describe all of the information available on the World Wide Web that cannot be found by using general-purpose search engines (Devine & Egger-Sider, 2009).
Reasons why this content can't be found include:
- Search engines can't reach it - it may be behind a paywall or firewall, or the site may have blocked search engine's webbots that index information on the web.
For example, most library databases are part of the invisible web as they are only accessible to staff and students who have logged into the library's subscription access.
- The content can't be read by search engine's webbots - for example files, videos, audio files or pictures without metadata written in html, which is what webbots read.
- Content is not linked from anywhere else or must be accessed by a separate search interface that search engines can't read.
Sources:
Devine, J., & Egger-Sider, F. (2015). Beyond Google: The invisible web. Retrieved from https://library.laguardia.edu/invisibleweb
oEDB. (n.d.). The Ultimate Guide to the Invisible Web. Retrieved from http://oedb.org/ilibrarian/invisible-web/
Taylor, McCartney. (2016). Deep web search: A how to site. Retrieved from http://deep-web.org/
Quality may also be an issue because it is often not peer reviewed or edited.