What's the name of the folded card in the book?

The folded cards in the book are called "bookmarks".

. A bookmark is a small piece of paper sandwiched in a book to record the progress of reading. With the development of the Internet era, electronic tags are derived to record reading progress and experience.

Bookmarks are not only paper, but also high-quality pure copper-zinc alloy raw materials, such as nickel-plated paint, sand-plated nickel, antique copper, pad printing, gold-plated paint, two-color electroplating, nickel-plated enamel, nickel-plated inlay and so on. This bookmark is called metal bookmark, which is an innovation in bookmark development. During the temple fair, you can see many metal bookmarks on Facebook, which represent the traditional culture of China.