The traditional East Asian calendars divide a year into 24 solar terms (節氣). Lìdōng (pīnyīn), Rittō (rōmaji), or Ipdong (romaja) (Chinese and Japanese: 立冬; Korean: 입동(S)/립동(N); Vietnamese: Lập đông; literally: "start of winter") is the 19th solar term. It begins when the Sun reaches the celestial longitude of 225° and ends when it reaches the longitude of 240°. It more often refers in particular to the day when the Sun is exactly at the celestial longitude of 225°. In the Gregorian calendar, it usually begins around November 7 and ends around November 22.
Lidong signifies the beginning of winter in East Asian cultures.