The shortest day of daylight per year.
A myriad of winter holidays happen during this time period, with many centered around Winter Solstice particularly. (Perhaps the ones that aren't specifically came to be to give us a little bright light in the darkest of winter nights.)
Here are two videos to brighten your day of limited light. One an overview of Winter Solstice that I created at Biteable.com, & the other a time lapse of the solstice from Fairbanks, Alaska, upwards toward the Arctic Circle. May these visual images help you enter the season ahead, looking for the brightness where you can find it as our daylight swings upwards, a litte bit with each passing sunrise & sunset.