Grey literature is generally understood to mean literature that is not formally published in common or conventional sources, like books or journal articles. It may be described as ephemeral, invisible, informal, underground, etc. - that is, literature that may be unevaluated and not peer-reviewed.
Including, but not limited to...
| Reports (including pre-prints) | Preliminary progress & advance reports | Institutional / internal reports |
| Research memoranda | Market research reports | Reports of commissions or study groups |
| Theses | Conference proceedings | Technical specifications and standards |
| Translations (not distributed commercially) | Official documents (issued in limited numbers) | Technical and commercial documentation |
