"The Fourth International Conference on Grey Literature (GL '99) in Washington, DC, in October 1999 defined grey literature as follows: "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."
In general, grey literature publications are non-conventional, fugitive, and sometimes ephemeral publications.
They may include, but are not limited to the following types of materials:
Types of Grey Literature list: growing list of examples
Due to the nature of grey literature, librarians have had difficulty acquiring and making it accessible. At The New York Academy of Medicine, there was a push by public health and health policy researchers for the Academy Library to obtain this type of material and to add it to the catalog (Gray, 1998). As a result, the Library acquires materials from various organizations publishing in these areas and gives them special cataloging treatment.
The Grey Literature Report is the first step in this initiative to not only collect these items for the Academy's collection, but to assist other librarians with collections in these fields in developing theirs."http://www.greylit.org/about
Please note that as of January 2017, the Grey Literature Report website and database will be discontinued and will no longer be updated, but the resources will still be accessible.
SOURCE: GreyNet International 1992-2017