A textbook is a book used for the study of a subject. People use a textbook to learn facts and methods about a certain subject. Textbooks sometimes have questions to test the knowledge and understanding of the learner.
A workbook is a type of textbook that has only practice questions and exercises. Workbooks are designed not to teach but to provide practice and to highlight areas which need more learning. A revision guide is a type of textbook that is used to remind the learner about the subject and give him/her extra practice, especially before an examination.
A textbook is usually lent to students by a school to accompany a course the school is teaching. Sometimes, especially at university, students have to buy the textbooks they need themselves or borrow them from a library.
Most textbooks are only published in printed format. However, some are now available online as electronic books.