What the Heck Is Metadata?
When we move a book into production, we ask every client to provide us with a completed form, called the "Production Checklist." The "PCL." It's a simple form in Word, with boxes to be filled out by you, as the publisher. Those boxes are "metadata." Using the PCL is optional. If you don't provide us with one, we'll simply embed the book name and author name in the metadata. If you do complete it, we'll embed all the information on the form (description, tags, subjects, etc.) inside the book, invisibly. (That's what "metadata" is for ebooks--information embedded inside a book that's invisible to the human eye, but is visible to search engines, to help them find your book in searches on the Net.)
This is one of the services that we include, as part of our Secret Sauce, to help our authors get their books sold, after they are published. For more information please read this article from PBS and Mediashift about metadata, and how it's used: PBS and Mediashift Article about Metadata and why we go to the trouble of adding to your book.
Too Long, Didn't Read--What Does That Mean for Me as an Author?
The short version is this: the description, tags, subject information, that you fill out on the PCL are put inside your book so that it can be found across the Internet by search engines. Some of these Search Egnines are able to search what is sometimes called "The Deep Web," which is merely web-geekery-speech for "databases." The upside, though, is that by using the embedded metadata, your book is more likely to be found by someone searching for a title in your area (genre, topic) than someone whose book only uses the metadata fields available to them at upload at Amazon, B&N and the like. It's simply part of our service.
Don't miss that MediaShift article--it's long, but it's worth the effort and the focus.