Grey literature is research published outside of commercial or academic publishing. Grey literature might not look like a traditional book or article. You may find it in the form of a PDF or report, for example, but the information included should still be high quality.
Examples of grey literature include:
Grey literature is an excellent source of recent research in many disciplines.
Industry and government bodies often produce grey literature and make it available online faster than other publication types.
It's important to check grey literature, like theses and dissertations, to see what research other people are producing in your field.
Grey literature does not go through the same peer-review process as a commerical publication, so it's important to check it.
Make sure you cross-check information sourced in grey literature against information derived elsewhere to ensure its quality.
Use the same skills you would use to evaluate any other material: