'Grey' or 'gray' literature is produced by organizations whose primary activity is NOT publishing. In other words, grey literature is basically any source that's not traditionally published. The term grey literature was coined to distinguish this type of literature from the so-called 'white' literature: the traditionally published scholarly literature that was historically printed on white paper.
Grey literature is thus not tied to or controlled by established publishers, and is usually published only online.
Grey literature typically comes from:
Grey literature includes, but is not limited to:
Wikipedia can serve as a convenient starting point for finding information on a new topic. Watch this short video that explains the advantages and disadvantages of Wikipedia, and how you can best make use of it [sound not required].