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:

• 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) (Alberani, 1990).

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"?  

• Typically published much faster then scholarly articles
• Has no formal peer-reviewed process
• Doesn't usually have a comprehensive literature review
• Often the "official author" is an agency or organization rather then an individual

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