Flatplan
Also called page plan, pagination plan
A plan of every page of a book as a row of thumbnails: what goes on each page, where the images fall, where chapters start. It is read in sections, often of 16 or 32 pages.
In practice
It is the tool for bringing the page count to a multiple of the section: a 150-page book will often cost as much as a 160-page one. It also helps group colour images in the same sections when the rest is black, which can lower the price. Show it to the printer before layout, not after.