In general, gray literature publications are non-conventional, fugitive, and sometimes ephemeral publications. They may include, but are not limited to the following types of materials:
Alberani V, Pietrangeli PDC, Mazza AMR (1990). The use of grey literature in health sciences: a preliminary survey. Bulletin of the Medical Library Association 78(4): 358-363.
How do scholarly articles differ from "gray literature"?
Using Statistical Insight to find reports. Statistical Insight is a unique library resource that allows you to discover reports from a vast array of agencies and organizations that allows you to search for information found in statistical tables from this gray literature.
Find reports from Interest groups, think tanks and research organizations