A sweater (more commonly known in Britain as a jumper) is a knit or crocheted clothing item for the upper body. Sweaters have a reputation and history of being purpose-created for cold environments & harsh weather.
The first of what we would today recognize as sweaters were knit by fishing villages on Guernsey - a Channel island near Normandy. Created at least as early as the 15th century, these 'guernseys' were made with tightly spun yarn so as to repel seawater and retain heat.
The design proved very popular among the people whom were exposed to it, and coastal communities throughout the British Isles and North Sea began to knit their own versions. Over time, the pronunciation of the name 'guernsey' shifted to 'gansey' and by the middle of the 19th century the Royal Navy had adopted the gansey into their official uniform.
Sweaters were popularized as a premiere fashion item in 1921, when the Prince of Wales was featured wearing a sweater vest knit in Fair Isle, kicking-off a demand craze for similar products. Then, in 1950, Vogue magazine wrote a feature on the Aran sweater - an act that almost single-handedly birthed Ireland's commercial sweater trade.
Both practical and trendy, learning how to knit a good sweater pattern will be a gift to yourself that just keeps on giving. Rare is the person who can't find a use for a new one.