In the old days (as I often say) there used to be subscription libraries, where you paid a small annual fee, and then paid a little more each time you borrowed a book. When you returned the the book, you were credited what you had paid for it, less a fee, and so you were encouraged to borrow another book, just to use up your credit. My mother used to work at one. She had an amazing customer list -- women from the upper echelons of our country town, who did not deign to be seen at the free public library.
Now, in this digital age, it is different. You pay a monthly fee to a subscription service, and can borrow eBooks for nothing. You don't return them, obviously -- I assume that when the loan time is up, the book simply vanishes from your eReader.
And, it seems, in the digital book world, it is the flavor of the month. As DBW says:
Apple's recent acquisition of book recommendation engine BookLamp suggests the company is considering a move into the now-hot ebook subscription service to compete with Amazon's new Kindle Unlimited, Scribd, Oyster and others.
Contrary to popular belief, a good recommendation engine isn't hugely important to a good ebook retail operation, writes Andrew Rhomberg. But, it's very important to any kind of content subscription service.
So, does that mean Apple is definitely going to have one? No. But if it does, you know where you heard it first.