noun, adverb
this winter; next winter; last winter
The meaning depends on context and tense. In present/future contexts, it usually means 'this winter' or 'next winter'. In past contexts, it can mean 'last winter'. Often used adverbially without a particle.
今冬は暖冬になる見込みです。
This winter is expected to be mild.
今冬、北海道へスキーに行く予定です。
I plan to go skiing in Hokkaido this winter.
We had a lot of snow last winter.