What is Perfect Paperback?

I just had a blogger email me wanting to know what "picture perfect" was in the book's description at Amazon and I thought I'd dig up some info in case you were wondering it too.  As you know, Amazon puts several formats up beside an author's book including Paperback, Kindle, that sort of thing but recently they've been adding "Perfect Paperback."  What is this?

Supposedly, perfect paperback is just another name for paperback binding.

I found this at the Wikibooks site:

"Perfect binding is not a stitch binding at all, but a solely adhesive based binding. It is the easiest and least durable way to produce books, and is how most paperback books are bound. Single leaves are jogged to form a straight block, and the spine edge is glued with PVA, or rarely, some other bookbinding glue.

So there you have it.  Not sure when Amazon started putting this up.  Anyone know?