What is a "rare book" diversion

It may be a bit late in the history of this project blog but here are a few definitions of a what makes a "rare book"
The National Library of Scotland
American Museum of Natural History
Rare Books and Manuscripts Section (RBMS) of the Association of College and Research Libraries

A "modern" rare book in our collection...
Howl : and other poems by Allen Ginsberg (RB 2371) was published in 1956. This is the first printing of one of the most important examples of Beat Poetry. Our copy is also signed by Ginsberg
Howell by Allen Ginsberg on YouTube