The doodle features a colourful hand knitting woollen clothes.
The winter solstice is a phenomenon which usually occurs on either December 21 or December 22. During the solstice in Northern Hemisphere the sun is at its greatest height from the South Pole.
Mashable .com says that the winter solstice isn't the full day of Dec 21, but rather occurs at a specific time. At that point, the sun is shining farthest to the south, directly over the Tropic of Capricorn.
Each year the phenomenon happens on a different date and at different time.
Across the world, people mark the day in various ways which even include rituals and festivals.