Winter Solstice or "Dongzhi" is the 22nd of the 24 solar terms. It usually arrives around December 21-23. The tropic of Capricorn is directly under the sun on this day, so it is the shortest day of the year in the northern hemisphere. After the Winter Solstice, the days start to become longer.
24 Solar Terms -- Winter Solstice
Source : People's Daily | Editor : Song Duer