I'm sure someone else on this board knows where the name "commonplace book" originated. I first heard of it on CBC when Bill Richardson started a "Commonplace book of the air" and invited listeners to phone in their entries.
A commonplace book is a book in which you write things that you find striking in your reading or conversations. A lot of what is in mine are witticisms, but I also have quotes from "Cold Mountain" and longish pieces on the nature of art, etc, things that I think "I love that, and I'd like to read it again without having to search thorugh the whole book for it" So instead I just search through books I've kept (on my third so far) and get sidetracked by other interesting things.
I make my own commonplace books, using whatever paper has grabbed my attention at the time. The one I'm currently using is covered with an off-white paper printed in burgundy with writing in, I believe, Thai. The paper was brought to me by a friend when she returned from a trip to SE Asia.
In an oxymoronic way, a commonplace book is actually quite extraordinary.