Like a person's ID number. 978-7-81076-841-7 is the book number. 978 stands for China and 7 stands for China. The following is a copy of Baidu Encyclopedia:

ISBN is an internationally accepted code for books or independent publications (except periodicals). Publishers can clearly identify all non-periodical books by the international standard book number. An ISBN has only one or one corresponding publication. If the new edition doesn't change much on the basis of the original edition, it won't get a new ISBN when it is published. When the paperback edition is changed to the hardcover edition, the original ISBN number should also be recovered.