Grey literature is information that is produced outside of commercial publishing channels. They include print and electronic material produced by organisations such as governments, educational institutions, business and industry associations.
Examples of grey literature include:
Theses and dissertations, conference proceedings, newsletters, reports, government documents, informal communications, translations, census data, research reports, technical reports, standards, patents, videos, clinical trials and practice guidelines, e-prints, preprints, wiki articles, emails, blogs, listserv archives, repository content and more.
Although grey literature is not usually peer reviewed, it may still be a good and reliable source of information for the review topic. It is necessary to evaluate everything you find. Here are some reasons why you should consider including grey literature in your search.
The AACODS Checklist is a useful tool for evaluating the quality of grey literature.
The Library's Find Statistics guide provides further details on finding relevant statistics by geographic location or topic.