A backpack, sometimes called a rucksack or knapsack, is a cylindrical bag carried on one's back. It is closed with a zipper or other fastening device, has a handle for carrying, and often has an outside strap for use while walking or hiking. It is one of the oldest styles of bag used by humans, dating from about 6000 B.C. Today a backpack may be made of fabric, leather, nylon, canvas, rubber or other materials. A backpack is one of the best ways to carry a large number of items.

A backpack is made up of individual compartments for various purposes, including protection and organization. It usually consists of two main sections: the main compartment is where the contents are stored; the back is where the straps are attached and the contents held. A typical backpack for work and gym is eight to ten inches deep and can hold up to forty pounds (nineteen to twenty-five kilograms). A rucksack has much more space for carrying items and for holding clothing, shoes, water bottles, other supplies, tools and equipment, and other personal items. A rucksack is useful for carrying objects such as books, shoes, clothing, and other items that need to be carried long distances.

A backpack is made up of a series of frames, which determine the shape and configuration of the bag. The most basic backpack consists of two cylindrical frames, one inside the other, with no external frame. The contents of the pack are held in the inner frame and are not visible from the outside, while the outer frame carries the visible contents of the backpack. Backpacks are also known as "backpack frames" or "backpack lines".

An alternative to having no frame is to have a strong upper or side frame. These frames add stability to the backpack straps. Frames that are solid have a reinforced bottom part that is attached to the frame on each side. When there are no upper frame and an upper frame with a reinforced bottom part, the backpack is known as a cantilever backpack. Cantilever backpacks have strong shoulders and are great for carrying items such as books and shoes.

A cantilever backpack has strong but lightweight shoulders. These are known as "attachment" shoulders. These shoulders make it easy to carry the backpack on the hips rather than on the shoulders. These types of backpacks also often have one or two attachment shoulder pockets which allow the wearer to keep items close to their body. The most common places for these pockets to be located are on the outside of the waist, the inside of the waistband, or inside some of the lower pockets.

Most backpacks have zippers at various locations on the back panel. Zippers on the outside of the backpack help the person wearing the backpack to more easily slip on and off the backpack as they are being moved. Some people prefer backpack zippers that are on the inside of the back panel because they believe this design provides a little more security.

Some backpacks have additional features such as deep-seating or pocketed hydration systems. Backpacks without shoulder straps can be worn as backpacks, while ones with straps can also be used as beach bags or hiking packs. Backpacks with detachable hip belt or adjustable hip belt straps allow for a variety of different looks. Many backpacks have outside drop pockets that can be used for small items that are not wanted in the main compartment.

Finally, when choosing your new backpack it is important to choose a backpack that is comfortable to wear and that is convenient for you. A back pack is basically a long sleeve bag designed to be carried over the shoulder. Backpacks are pretty self-explanatory; they just have pockets and straps. The most important feature to consider when purchasing a backpack is how comfortable you are carrying it around. If you have a small frame, then make sure the backpack does not cut into your shoulders and if you have a large frame to make sure there is enough room to comfortably carry the backpack without folding or creasing your clothes.