UW Worldcat is especially useful when you want to search as broadly as possible for a topic or when you are seeking a relatively rare item that isn't likely to be available at the UW. It also facilitates borrowing books from other libraries.
A technical defintion...
"That which is produced on all levels of govenment, academics, business and industry in print and electronic formats, but which is not controlled by commercial publishers."
(Fourth International conference on Grey Literature, Washington D.C., October 1999)
Examples of grey literature may include:
Market research reports
Newsletters and/or bulletins
Dissertations & Theses
Examples of why you might use grey literature: