The term “laid in” refers to a loose paper sheet inserted into a book. The primary purpose of a laid-in sheet is twofold: it can act as a bookmark, and it often contains unique information about the book not found elsewhere in the text.
Typically made of thin, brightly colored paper so they are easily visible when flipping through pages, laid-in sheets often contain printing on both sides; one side relates information about the book, while the other might feature an image or graphic design. Publishers sometimes insert such sheets in-house before shipping books to their destinations; authors may include them with preordered or signed books; readers even tuck them inside at home.
The term “laid in” applies more broadly than just to sheets but rather any objects placed inside a book — bookmarks, bookplates, or even photographs.
To bind something into a book means to sew or glue it into the binding during manufacture. To lay something in means to insert it loosely into the binding after manufacture.
Laid in objects are more secure than bound-ins and can work loose or become detached altogether over time. For this reason, they’re typically used for items that don’t need to be permanent—such as bookmarks, advertisements, and similar ephemera—or for things like photographs that have their protective covering and thus don’t necessarily need additional attachment points.
Laid in objects can also be used for repairs—for example, if a page has become torn or otherwise damaged beyond repair (think coffee spill)—a new page can be laid in place without disassembling and rebinding the entire volume.