The writer Umberto Eco belongs to that small class of scholars who are encyclopedic, insightful, and nondull. He is the owner of a large personal library (containing thirty thousand books), and separates visitors into two categories: those who react with “Wow! Signore professore dottore Eco, what a library you have! How many of these books have you read?” and the others — a very small minority — who get the point that 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.
Black Swan – Nassim Nicholas Taleb

I have had a similar experience about myown book collection. People expect that if you have books then you must have read them. But this is exactly what I hold the books for, a reference tool for further knowledge. And then they have a beautiful word in Japanese which describes the spirit in which you buy more unread books.

Tsundoku:buying books and not reading them; letting books pile up on shelves floors or nightstands