backlist
Books that were not recently released, but are still available for purchase.
Backlist books don't attract the attention that new releases do, but backlist books that sell solidly over a number of years can be an important part of an author's income stream.
In print publishing, most backlist books would eventually go out of print once they were no longer selling a sufficient number of copies to justify the cost of printing and stocking them.
When print-on-demand is combined with online sales, backlist books can remain available for a longer time because of lower printing and stocking costs.
In e-publishing, the backlist can be sold almost indefinitely, because the cost of storing, copying, and transmitting the e-book file is negligible.
Also see: print publishing, print-on-demand, e-publishing, out of print.