The size of a book is generally measured by the height against the width of a leaf, or sometimes the height and width of its cover. A series of terms is commonly used by libraries and publishers for the general sizes of modern books, ranging from folio (the largest), to quarto (smaller) and octavo (still smaller). Historically, these terms referred to the format of the book, a technical term used by printers and bibliographers to indicate the size of a leaf in terms of the size of the original sheet. For example, a quarto (from Latin quarto, ablative form of quartus, fourth) historically was a book printed on a sheet of paper folded twice to produce four leaves (or eight pages), each leaf one fourth the size of the original sheet printed. Because the actual format of many modern books cannot be determined from examination of the books, bibliographers may not use these terms in scholarly descriptions.