Alternative names include haversack from the German Hafersack meaning "oat sack", (which more properly describes a small cloth bag on a strap worn over one shoulder and originally referred to the bag of oats carried as horse fodder), Kraxe (a German rucksack with a rigid framework), and bergen (a large load-carrying rucksack, from a design issued by the British Army during the Second World War).
Backpacks can often simply be referred to as "packs", especially in outdoors contexts; though sometimes ambiguous compared to other bags such as saddlebags and duffel bags, context is generally sufficient for identification.
A backpack — also called bookbag, kitbag, knapsack, rucksack, pack, sackpack or backsack — is, in its simplest form, a cloth sack carried on one's back and secured with two straps that go over the shoulders, but there can be variations to this basic design.
Lightweight types of backpacks are sometimes worn on only one shoulder strap.
The external frame is typically made from aluminum, other lightweight metal alloy, and recently reinforced synthetic polymers or plastic and is equipped with a system of straps and tautly-stretched netting which prevents contact between the metal frame and user's back.
In addition to comfort, this "stand-off" provides the additional benefit of creating air circulation between the frame and the wearer's back.
They are also used in recreational activities, and have long since been used to carry sports equipment and other materials.
Backpacks in general fall into one of four categories: frameless, external frame, internal frame, and bodypack.
In German, Rücken means "back" and Sack means "bag".running, cycling, hiking and hydration), usually offload the largest part (up to about 90%) of their weight onto padded hip belts, leaving the shoulder straps mainly for stabilising the load.This improves the potential to carry heavy loads, as the hips are stronger than the shoulders, and also increases agility and balance, since the load rides nearer the wearer's own center of mass.The name rucksack is cognate with the Danish rygsæk, Norwegian ryggsekk, Dutch rugzak, Afrikaans rugsak and Swedish ryggsäck.The word knapsack was the usual name for a rucksack or backpack up until the middle of the 20th century.