Cover: One of the external features of a book is its cover. The cover usually includes the title, author, publisher, publication date, ISBN number, pricing, copyright page and other information.

2. Binding: The binding of books refers to the overall design and production process of books, including cover materials, printing methods, fonts, colors, typesetting, illustrations, etc.

3. Layout: The layout of books refers to the layout design of books, including the arrangement and layout of words, illustrations, pictures and charts.

4. Size and weight: The size and weight of a book is also one of its external characteristics. Different types of books, such as novels, textbooks and magazines, may have different sizes and weights.