It's a mix of a jacket, sweater, and a shirt.
You know, for those days when it's not super hot or super cold. But it's good for when it's cold and hot, but not at the same time.
It's a pretty thin hoodie, without a zipper, can be with or without pocket. Usually not worn with a shirt underneath.
"I just got a new shwacket!"
"Woah, is it steezy?"
"Of course it is!"