"In bookbinding, a dos-à-dos binding (from the French meaning "back-to-back") is a binding structure in which two separate books are bound together such that the fore edge of one is adjacent to the spine of the other, with a shared lower board between them serving as the back cover of both. When shelved, the spine of the book to the right faces outward, while the spine of the book to the left faces the back of the shelf; the text of both works runs head-to-tail." (Straight from Wikipedia!)
