Grey literature refers to both published and unpublished research material that is not available commercially. In general, grey literature publications are non-conventional and sometimes ephemeral publications that are not indexed in databases such as PubMed and Embase.
Grey literature includes:
IOM Standard 3.2.4 states: that researcher should "Handsearch selected journals and conference abstracts." Handsearching can be done of either paper or electronic journals and involves a page-by-page search. Reasons for handsearching include: