A backpack—also called knapsack, rucksack, rucksac, pack, sackpack, booksack, bookbag or backsack—is, in its simplest frameless form, a cloth sack carried on one's back and secured with two straps that go over the shoulders, but it can have an external frame, internal frame, and there are bodypacks.

Backpacks are commonly used by hikers and students and are often preferred to handbags for carrying heavy loads or carrying any sort of equipment, because of the limited capacity to carry heavy weights for long periods of time in the hands.