Here’s a simple, clear description of a school bag:

A school bag is a sturdy, portable bag used by students to carry books, notebooks, stationery, and other school supplies. It usually has two adjustable shoulder straps so it can be worn comfortably on the back. Most school bags are made from durable materials like nylon or canvas and include several compartments—such as a main pocket for books, a front pocket for smaller items, and side pockets for water bottles. Many also have zippers, padded backs, and sometimes decorative designs or colors that reflect the student’s style.