Winter solstice is the shortest day of the year, with the least hours of sunlight within the 24 hour period. Which means it’s a rather depressing day.
This video explains the science behind the winter solstice, with the planet we all live on tilting the furthest away from the sun. At least in the northern hemisphere. In the southern hemisphere it’s six months later (or earlier).
Winter solstice is actually today (Dec. 22) although there seems to be some confusion over the date. It falls on a day between Dec. 21 and Dec. 23 each year, although it most often lands on Dec. 21.
Winter solstice is an important date in the calendar for many cultures and religions. It’s no coincidence that Christmas is celebrated just a couple of days later.