The twenty-four solar terms divide the ecliptic into equal arcs of fifteen degrees, and this one falls at 210 degrees of the sun's apparent longitude. It is a major term, a zhongqi, one of the twelve that fall in the even positions of the twenty-four. The major terms are the ones that anchor the lunar months, and they alternate strictly with the sectional terms, so a zhong is always followed by a jie fifteen degrees later.
The system travelled with the Chinese calendar. Japan, Korea and Vietnam all adopted the twenty-four terms and kept their own readings of the same names, and the terms remain in use in each. In 2016 the twenty-four solar terms were inscribed on the UNESCO Representative List of the Intangible Cultural Heritage of Humanity, on the ground that they remain a living framework for agricultural and everyday practice rather than an obsolete scheme.
Shuangjiang, the descent of frost, closes the autumn group and completes the sequence that begins with the white dew and passes through the cold dew. It is the last of the terms before winter opens at Lidong, and its name is the point at which the graded progression of the autumn terms reaches something that will damage a crop rather than merely mark the season.