Daehan (Kor. 대한, Chin. 大寒, lit. Great Cold) is the last of the twenty-four solar terms. It occurs in the end of the twelfth lunar month and is around January the twentieth on the Gregorian calendar. The sun around this time is situated at an ecliptic longitude of 300°.

Winter cold intensifies progressively after Ipdong (Kor. 입동, Chin. 立冬, Onset of Winter), with temperature hitting new lows successively on Soseol (Kor. 소설, Chin. 小雪, First Snow), Daeseol (Kor. 대설, Chin. 大雪, Snow Blast), Dongji (Kor. 동지, Chin. 冬至, Winter Solstice), and Sohan (Kor. 소한, Chin. 小寒, Minor Cold). Although in China, Daehan is said to be the coldest time of a year, this is not the case in Korea, where winter cold hits its peak around Sohan. Hence, the weather tends to be milder on Daehan than on Sohan, as attested by the old sayings: “If it is not cold, it’s not Sohan; if it is not mild, it’s not Daehan, ” or “The ice of Sohan melts on Daehan.” People in Jejudo, Korea’s southernmost island, call the approximately one-week period from the fifth day after Daehan to the third day before Ipchun (Kor. 입춘, Chin. 立春, Beginning of Spring) singugan (Kor. 신구간, Chin. 新舊間, lit. between the old and new). This period is believed by the islanders to be a special window of time where activities such as moving or repairing a house can be conducted with no adverse consequences for the family.

Source: https://folkency.nfm.go.kr/kr/topic/detail/3587