From Longman Dictionary of Contemporary EnglishISBNISBN /ˌaɪ es biː ˈen/ noun [countable] TCN (International Standard Book Number) a number that is given to every book that is publishedFrom Longman Business DictionaryISBNISBN noun [countable]COMMERCE International Standard Book Number; a code number that all copies of a particular book have, and which is used especially when ordering copies of the book