der Pullover
sweater
A knitted or woven item of clothing for the upper body with long sleeves, usually worn over a shirt or T-shirt.
Im Winter trage ich gerne einen dicken Wollpullover.
In winter, I like to wear a thick wool sweater.

sweater
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sweater
A knitted or woven item of clothing for the upper body with long sleeves, usually worn over a shirt or T-shirt.
Im Winter trage ich gerne einen dicken Wollpullover.
In winter, I like to wear a thick wool sweater.

The word 'Pullover' (sweater) comes from English and is derived from 'to pull over' (to put on over something). So it literally describes a piece of clothing that you pull over your head and other clothing.
Zieh dir einen Pullover an, es wird kühl draußen.
Put on a sweater; it's getting cool outside.
In colloquial language, 'Pullover' (sweater) is very often shortened to 'Pulli' (sweater). This form is widespread and sounds more informal.
Wo ist mein blauer Pulli? Ich kann ihn nicht finden.
Where is my blue sweater? I can't find it.
Because it is a piece of clothing, 'Pullover' (sweater) is often used with the verbs 'tragen' (to wear), 'anziehen' (to put on), and 'ausziehen' (to take off).
Er zog seinen nassen Pullover sofort aus.
He immediately took off his wet sweater.
jacket
'die Jacke' and 'der Pullover' are both items of clothing for the upper body and can keep you warm. But they are worn differently. A jacket is usually worn over other clothing and often outdoors; you can normally open it at the front and take it off when you go inside. A sweater is pulled on over a shirt or T-shirt and often stays on indoors too. Learners may confuse the words because both have long sleeves and help against the cold. A simple guide: 'Jacke' for outside over everything, 'Pullover' as a warm layer of clothing on the body.

Beim Frühstück trägt Tom einen dicken Pullover.
At breakfast, Tom is wearing a thick sweater.
Im Büro ziehe ich meine Jacke aus, weil es dort warm ist.
At the office, I take off my jacket because it is warm there.