What the Hell Are Used E-books?

What the hell, indeed, are used e-books?

I've been reading more than a few articles about Amazon's latest conquest: a patent they filed for in 2009 and won on January 29 this year that would somehow allow them to sell used e-books. The only problem is that most people don't seem to know what used e-books are. This is from Publisher's Weekly:

Amazon’s business model has long been dependent on resellers of used books and other merchandise. But a U.S. patent that Amazon Technologies in Reno, Nev.,...