Sweater

A sweater is a garment that was designed to replace shirts as women's loungewear, but to make her parents happy, the inventor claimed that sweaters were made for sweating in. They were not. Sweaters are almost always worn without pants when worn by girls, which is 99.9% of the time.

History
Back in the 1970s, a random teenage girl didn't want to wear shirts because they were too short, so she knitted a shirt with long sleeves that she could pull over. This ended up with both sweaters and long-sleeve shirts being invented.

Style
Sweaters should be worn with skirts or without an accompanying garment. Sweaters should never be worn with pants. That's illegal!

Uses
Sweaters are used as women's loungewear. Sometimes, they're the only garment besides lingerie (whatever the fuck that means) in porn films of women masturbating. Unfortunately, I couldn't find any good pictures of the latter, so please take these two gifs of anime girls masturbating.

Sweater curse
Some girls believe in a "sweater curse" that if a girl wears sweaters without pants every day for a year, then they will physically be unable to wear dresses, skirts that are worn without a sweater, and pants. Luckily, a cure for this was invented in the 1990s, but people still believe in it because 99% of images of girls wearing sweaters are of girls wearing sweaters but without pants. Frankly, 90% of those are of girls masturbating in or stripping out of oversized sweaters (without wearing pants, of course!).