It's a old form of displaying you stamps in a book. This would be a light mark on back of stamps. These stamps are new and they do not have a hinge mark on the back of them, which is good. Now sometimes the covers that is used to display stamps, will have a hinge mark on them in order to display them in a book. Now that is ok. I hop that helps you to understand. It is fun to collect stamps, you learn a lot about history of that country.