I don't like this term. All the best libraries contain books waiting to be read. The term "antilibrary" suggests something that stands in opposition to the library, like a Board of Censorship or book-burning fascists. Taleb makes an excellent point in the quoted passage, but he's hit on the wrong term. But why do the books look at you menacingly? My unread books (and they are many) look at me invitingly.
A private library is not an ego-boosting appendage but a research tool. Read books are far less valuable than unread ones. The library should contain as much of what you do not know as your financial means, mortgage rates, and the currently tight real-estate market allow you to put there. You will accumulate more knowledge and more books as you grow older, and the growing number of unread books on the shelves will look at you menacingly. Indeed, the more you know, the larger the rows of unread books. Let us call this collection of unread books an antilibrary.
—Nassim Nicholas Taleb, The Black Swan, Random House, April 17, 2007