Grey literature is material that is not produced by commercial publishers. It is produced by governments, local authorities, health boards, research groups, professional associations, charities, not-for profit organisations, companies etc. It may not be indexed in bibliographic databases and this can make it hard to find. There are many definitions of grey literature, for example:
The term grey literature is generally used to describe materials not published commercially or indexed by major databases.
Olson, C.A. (2015) ‘Using the Grey Literature to Enhance Research and Practice in Continuing Education for Health Professionals’ Journal of CEHP, 33(1), pp. 1-3.
Examples taken from GreyNet International (2021) Available at: http://greynet.org/greysourceindex/documenttypes.html (Accessed 21st December 2021)
You need to evaluate grey literature as it: