Leaf, Page, Recto, Verso
Here’s something I used to know but forgot at some long-ago point. The sheets of paper in a book are called leaves. One side of a leaf is called a page (that much I remembered). The front side of a leaf (the odd-numbered page on the right side of an open book) is called a recto. The back side of a leaf (the even-numbered page on the left side of an open book) is called a verso.
Why do you need to know this? Well, maybe you don’t need to know this, but don’t you feel just a little bit smarter now that you do? And I have just proven that you can find some interesting stuff by randomly leafing through the pages of The Chicago Manual of Style. As if you needed me to tell you.
(See Chicago 1.3 for this particular little tidbit.)