Gray literature basically refers to the wealth of information sources that are not published through traditional publishing houses. This basically includes any information source that is not a book, journal, magazine, or newspaper.
Gray Literature includes materials that are generally
According to the Twelfth International Conference on Grey Literature, the definition is as follows:
"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 libraries and institutional repositories, but not controlled by commercial publishers; i.e., where publishing is not the primary activity of the producing body" (for more information see Towards a Prague Definition of Grey Literature - PDF).