Winter vacation/holidays; the break during winter (often includes year-end and New Year period).
高校は来週から冬休みに入る。
High school will start winter vacation from next week.
冬休みに家族と温泉旅行に行く予定だ。
I'm planning to go on a hot-spring trip with my family during the winter break.
大学の冬休みは学部によって長さが違うことがある。
The length of university winter vacations can vary depending on the faculty.