A red exercise book is a type of notebook used for writing, typically in a school setting. It is called an "exercise book" because it is often used for completing written assignments or exercises. The red color of the book may be for decorative purposes, or it may serve as a way to distinguish the book from others in a student's backpack or desk. Exercise books are often small and portable, making them convenient for students to carry with them to class and use for taking notes or completing assignments.