Excerpt from The Writing World Defined--A to Z:
Acceptance letter. A letter from a publisher accepting your submission. Such a letter from a periodical will typically indicate the editor wants to buy your manuscript, what the payment will be, whether the payment will be on acceptance or publication, what rights they are buying, and perhaps in what edition of the periodical the piece will appear. Although some publishers will still send this letter by snail mail, the majority now do it by email.
With a book publisher, the initial submission will usually be a book proposal. In that case, the first acceptance letter will indicate the publisher is willing to look at your full manuscript—not that he is committing to buying it. If the initial submission was the full manuscript, the acceptance letter will usually indicate their desire to purchase your manuscript, and it may arrive with a copy of the contract or a list of basic terms they will be offering in a contract, along with any other details you need at that point. This Website lists some publishers open to accepting books at this time: http://myperfectpitch.com/book-publishers-accepting-submissions, and http://www.christianpublishers.net/?page_id=846.