The traditional East Asian calendars divide a year into 24 solar terms (節氣). Dōngzhì (pīnyīn) or Tōji (rōmaji) (Chinese and Japanese: 冬至; Korean: 동지; Vietnamese: Đông chí; literally: "winter's extreme") is the 22nd solar term, and marks the winter solstice. It begins when the Sun reaches the celestial longitude of 270° and ends when it reaches the longitude of 285°. It more often refers in particular to the day when the Sun is exactly at the celestial longitude of 270°. In the Gregorian calendar, it usually begins around 21 December (22 December East Asia time) and ends around 5 January.
Along with equinoxes, solstices (traditional Chinese: 至點; simplified Chinese: 至日; literally: "extreme sun") mark the middle of East Asian calendar seasons. Thus, in "冬至", the Chinese character "至" means "extreme" and the term for the winter solstice directly signifies the summit of winter, as "midwinter" is used in English.
In China, Dongzhi was originally celebrated as an end-of-harvest festival. Today, it is observed with a family reunion over the long night, when pink and white tangyuan are eaten in sweet broth to symbolise family unity and prosperity.