An exercise book is a type of notebook that is often used by students to write down notes, assignments, and other work during class or while studying. Dark blue exercise books are simply exercise books that have a dark blue cover. They are typically made of paper and have pages that are ruled, or lined, to make writing and organizing notes easier. Some exercise books may also have a hard cover, or be spiral bound, to make them more durable and easier to use. Exercise books are an essential tool for many students and are used to keep track of their work and progress.