In print, according to Oxford English Dictionary, means “on sale at the publisher’s, not yet sold out”. Out of print is defined as “no longer to be bought at the publisher’s, sold out”.
When our modern language was being born these words had a fairly obvious and unambiguous meaning. You could go along to the publisher’s warehouse (or in those days the bookseller’s) and see if there really were any copies to be bought. If there were none, and there was no prospect of any in the future, you would be justified in taking that to mean that the book was indeed “out of print”.
When books were printed by letterpress publishers tended to print once only. Of course there were lots of best-seller exceptions, but the vast majority of books would be printed in a run which, in the publisher’s best judgment, would last for ever, or at least until there was nobody left who wanted to buy the book. This was because when you print by letterpress you have to have type to print from. Once the book was printed the type would be “distributed”. Distributing type meant that the individual letters would be put back each in their own box ready to be used in the next job. By the twentieth century, when hand setting was just a memory, “dissing” type would be more likely to mean melting it down so that the metal could be reused to cast type for an entirely new job. Either way it was impracticable to keep the type “standing” for all of your books: there simply wasn’t space to store it (or capital to fund it). This fact is what led to the bibliophilic habit of collecting different “editions” of books: in the 19th century and earlier a reprint was referred to as an edition. Because the type would have been dissed off press, the decision to reprint necessitated resetting the entire book — with the wonderful opportunity for a whole set of new errors to creep into the text.
However even in that world publishers tended to put a special spin on the term “out of print”. Clearly, and justifiably, if the book sold faster than you expected and went out of stock before you had had time to reprint, there would be a period when the book was unavailable for sale – not because it was “out of print” but because it wasn’t back in print yet. As the relationship between author and publisher was put onto a more formal legal basis, this sort of problem needed to be addressed. Over time a convention evolved that the state of being “out of print” was not some empirically testable condition as described in the dictionary definition above, but a stage in a book’s life determined by the publisher, and accompanied by a probable reversion of rights to the author. In this world, out of print would have been defined as “having reached a point where it has been decided never, under any circumstances, to offer the book for sale again”. Stops on the way to that condition would be “Reprint under consideration” “Out of stock indefinitely” “Temporarily unavailable” “New edition under consideration” “Paperback under consideration” and other euphemisms for “we have no stock and aren’t doing anything about it, but we’re damned if we’ll revert rights to the author because we really hope to be able to make more money out of this book later on, once we’ve figured out how to do that”.
This meant that many books were never made OP. And there was also the halfway house of declaring the book out of print but not reverting rights to the author. Publishers who did this, and that probably means all of them, can now look through their out of print lists and select titles which they can reissue as print-on-demand books, thus generating income from minimal expenditure off books which have been dead for years.
Now of course all of that is out the window too, and we live in the brave new world where books can be available in perpetuity though digital printing and a true print-on-demand program (not to mention on-line distribution and Google Books). A book in a print-on-demand program is not “in print” in the sense that you could go along to the warehouse and look at the copies available for sale, but it’s certainly not out of print either. Authors’ agents are not happy, since they used to like to use the reversion of rights when a publisher put the book OP as an opportunity to negotiate a new deal with a different publisher, with a new advance attached to it. Of course contracts have not usually specified a number of copies to be printed, and it has been really irrelevant to the author whether the print quantity is 10,000 at one time or ten printings of 1000. In a conventional world the difference in print run is what makes the difference in profit (if all the books are sold) and is at the heart of the publisher’s business judgment. Now with print-on-demand the print run is one, or three, or whatever, just depending on what the customer’s order may call for. There is no quantity which the publisher can’t afford to print, so no point at which the book will become unavailable.
Does this mean that publishers are cheating their authors? I have to say I suspect not. If a book really has the potential to be resold to a different publisher for a sum of money which is worth fighting over, then the chances of its sale being so low that its publisher decides to put it into a print-on-demand program are slight. On the plus side, the author’s book continues to be available and to generate royalty income on a level of sales which in the old days would have meant that the annual royalty check would have been for $0, since no reprint that small could have been afforded.