For the Northern Hemisphere, the winter solstice occurs every year on December 21 or 22. (The Southern Hemisphere’s winter solstice occurs in June.)

The winter solstice is the day with the fewest hours of sunlight throughout the year, making it the “shortest day” of the year. Thankfully, after we reach the winter solstice, the days begin to grow longer and longer again until we reach the summer solstice—the first day of summer and the longest day of the year.
Think of it this way: Although the winter solstice means the start of winter, it also means the return of more sunlight. It only gets brighter from here!

This is all thanks to Earth’s tilted axis, which means that at the solstice, half of Earth is pointed away from the Sun, and the other half is pointed towards it.

https://www.almanac.com/content/first-day-winter-winter-solstice