Q. What is grey literature?
In general, grey literature (GL) publications are non-conventional, fugitive, and sometimes ephemeral publications. They may include, but are not limited to the following types of materials:
Reports (pre-prints, preliminary progress and advanced reports, technical reports, statistical reports, memoranda, state-of-the-art reports, market research reports, etc.), theses, conference proceedings, technical specifications and standards, non-commercial translations, bibliographies, technical and commercial documentation, and official documents not published commercially (primarily government reports and documents)
For more information on Grey Literature follow the link below.