What is gray literature?
Grey literature refers to literture that is not formally published in sources such as books and journals. Grey literature includes but not limited to conference abstracts or papers, hard to find studies, reports, or dissertations, governmental or private sector research, ongoing or unpublished clinical trials, technical reports, press release, white papers, fact sheets, brochures, or policy briefs.
According to APA rule (see APA book 7.03, p. 205-206 or APA style guide to electronic references, p. 19-21), formatting gray literature as you would a book. Some examples are citing IOM report, CNL white paper, and fact sheet.