The term "gray literature" (or grey literature) refers to any scholarly works that are not published in the traditional sense. These can include conference proceedings, government reports, technical standards, theses and dissertations, and unpublished clinical trials. Essentially, any research or relevant documents not intended for formal publication through commercial and/or academic channels can be considered gray literature. Despite its unpublished status, gray literature can be an important part of the body of knowledge about a given topic. Below are some examples of places you can find gray literature.
While these sources are all important, a broad internet search can also be helpful. Here are some resources on using popular search engines like Google for finding gray literature.