What is a "knapsack"?

A knapsack is a type of backpack that is typically made of canvas or leather and has shoulder straps and a closure system that is secured with buckles or drawstrings. Knapsacks are designed to be carried on one's back and are often used for hiking or camping, as they provide ample storage space for outdoor gear and equipment. They can also be used as a school bag or for general everyday use, and come in a variety of sizes and styles to suit different needs and preferences.