How long must a manuscript be before it is called a book? I am looking for an authoritative group or company to with the answer. Here is a few examples of authoritative companies or groups on this subject: Readers Digest, Ziff Davis, Penguin books, Barns and Nobels or American Book Publishing Association.
The best I have been able to come up with at this point is a magazine called Writer's Digest (WD) says 60K words. While WD is an authoritative source on the issue, I am looking for some one a bit more visiable then WD is.