A knapsack, commonly known as a backpack, is a type of bag that is carried on the back. It typically features two shoulder straps and is designed to hold various items, making it convenient for travel, school, or outdoor activities. Knapsacks come in various sizes and styles, often made from durable materials to withstand wear and tear. Backpacks are popular among students, hikers, and travelers due to their hands-free design. They can accommodate books, clothing, and gear, and often include additional compartments for organization. Many modern backpacks also have features like padded straps and ventilation for comfort during extended use.