Grey literature can be defined as:
"Any publication created outside recognised academic or commercial outlets and difficult to classify"
"Grey literature stands for manifold document types produced on all levels of government, academics, business and industry in print and electronic formats that are protected by intellectual property rights, of sufficient quality to be collected and preserved by library holdings or institutional repositories, but not controlled by commercial publishers i.e., where publishing is not the primary activity of the producing body."
(Joachim Schöpfel, Twelfth International Conference on Grey Literature, 2010).
Some grey literature is open access but not all open access resources are grey literature. And some contain both grey and white literature. Here is the link to our Open Access Resources Subject Guide.