A textbook is a comprehensive and authoritative guide on a specific subject, typically used as a reference work in schools or universities. It provides detailed information about a particular topic, often presented in an organized manner with clear explanations, examples, illustrations, and exercises to help students understand the material better. Textbooks are usually written by experts in their field and undergo rigorous review processes before being published. They serve as a reliable source of knowledge and provide a standard framework for teaching and learning.