Release Date Vs. Publication Date

The official publication date for my book is December 9th, but today I found out the book's release date is November 19th, meaning the novel will ship out on Nov. 19th to bookstores and libraries across the realm. I didn't even know there was a difference in dates, assuming that the publication date was the date the book would be in bookstores. I skimmed the Internet and gathered that a publication date is actually a more legal-type thing, used in book contracts and such to define a time when a book should be published by the publisher. Although, many publishers get around this official date by providing loopholes in the contract and thus give themselves leeway on when (the actual calender date) they publish a book.

I know. Not exactly clear, is it? Let's just say, I'm very happy the book will be "released" in time for the full holiday shopping season, and I will have a "publication" party/reading on or around Dec. 9th.