A backpack (also called rucksack, knapsack, packsack, pack, Haversack, or Bergen) is a cloth sack put on somebody’s back. It usually has two straps that go over the shoulders. It is used to carry things in it, and it often has many compartments to carry things. … Backpacks are also be used in the military by soldiers.
bag. A bag is a lightweight, flexible container meant for carrying things. … You can also refer to a suitcase, handbag, or purse as a bag. When the word is used as a verb, it can mean “to put in a bag,” but also “to catch something.” Figuratively, you can “be left holding the bag,” which means to be swindled or cheated.