A book is a form of written communication that contains text or images. It can be published on paper, in hard or soft covers or in digital form like ebooks. Books are commonly used in education, for entertainment and as a source of knowledge. They are categorized into different types, including fiction (containing imaginary content) and non-fiction (containing content that represents truths). They are also classified into smaller categories such as children’s books meant for specific age groups and reference works that gather collections of information into one volume.
Books can be a useful means of recording and transmitting information, as they are portable and durable enough to survive for long periods of time. They can be read and interpreted by people, irrespective of their literacy level. Books are often divided into several chapters and sections, and the contents are segmented into parts to facilitate assimilation. They can also be categorised into genres and sub-genres depending on the subject matter.
Although the book has many uses, its primary function is to announce, expound, preserve and transmit knowledge and information from one person to another. This is done on materials that are light and durable enough for comparatively easy portability, and has been the dominant medium for communication in all literate societies.
A temple column with a message carved on it is not a book, nor are private documents such as diaries or journals. Neither are handwritten notes or lists, as these do not have the same permanence and portability as the printed book.
Most modern books are printed by offset lithography on sheets of paper that are cut to standard sizes, known as trim sizes, which were established 200 or 300 years ago and have become the industry standard. The most common trim size is octavo, followed by quarto and folio. Other trim sizes are used for rarer books and specialised purposes.
In addition to the printing process, a book is usually bound into its final form. This is normally accomplished by “case-making”, which takes place off-line and prior to the books arriving at the binding line. This entails placing two pieces of cardboard onto a sheet of cloth into which is glued a thinner board cut to the width of the spine of the book. The resulting case is then ready for the book to be bound into it.
Most commercial publishers in industrialized countries assign ISBNs to their books, which is the internationally recognized standard for identification of book titles and is used for cataloguing, circulation and inventory control. In libraries, books are given coded numbers based on a library classification system and assigned positions on shelves according to their call number. Some books, particularly those of a very small print run, may not be assigned an ISBN, in which case the publisher’s catalogue number is recorded on the spine. A book with an unassigned ISBN is sometimes considered an out-of-print title. This is because it may be difficult to locate and obtain copies of the work.