Section
Also called signature, quire, 16-page section
A sheet printed on both sides and then folded, forming a group of pages: it is the unit a book is made of. How many pages a section holds depends on the format and the folding; a sheet folded into eight leaves, for instance, gives a 16-page section.
In practice
Ask the printer how many pages to a section the book is planned in before you settle the page count. The book is put together section by section, sewn or glued; a page count that does not come out even leaves blank pages at the end, or calls for a section of another size. A 200-page book in 16-page sections, for instance, comes to twelve and a half sections. Ask which solution the quote assumes.