In the United States, "backpacks" are commonly used for large backpacks (50 liters and above) for serious hikers. In this case, the smaller package (with a capacity of 20 to 30 liters) is usually called a "backpack" (only carry what you need for a day trip). However, these are also general terms for backpacks.
If we look at the backpack, there is no big difference now except English. Obviously, this is a sack (bag) and bag for carrying. As the name suggests, a backpack is a bag that carries your backpack. Although Americans did not invent backpacks, we still coined this term. In the United States, we often use children's school bags as backpacks. But in a broader sense, the backpack will be enough to meet the travel needs of a day or weekend.
Backpacks usually have two shoulder straps. But on an ideal backpack, the shoulder straps actually hardly bear any weight. Instead, the weight is mainly transferred to the cushioned hip belt. Why wear a belt?
If worn correctly, the belt can transfer the weight of the backpack from the shoulder to the hip. You can almost bear the burden of the body's largest muscle, the leg. However, the waist belt must be long enough to cover the front side of the hip bone, not the waist.
There are many kinds of backpacks. Like a tool backpack, fishing backpack or ordinary daily backpack.