A backpack is a bag with two shoulder straps designed to be carried on your back, leaving your hands free. The design distributes weight evenly across both shoulders, making it easier to carry books, supplies, or gear for long periods.

Students use backpacks to haul textbooks, notebooks, and lunch to school each day. Hikers pack them with water, snacks, and emergency supplies for mountain trails. Travelers might stuff a backpack with clothes and a camera for exploring a new city.

Some people call it a knapsack or rucksack, though backpack is most common in American English.

Modern backpacks often have multiple compartments, padded straps, and special pockets for water bottles or laptops. The basic concept, though, goes back centuries: soldiers and travelers have always needed ways to carry supplies while keeping their hands available for climbing, working, or defending themselves. Today's colorful school backpack descends from those practical designs.