The twenty-four solar terms divide the ecliptic into equal arcs of fifteen degrees, and this one falls at 180 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 twelve major terms are what make the Chinese calendar work as a lunisolar one. Each ordinary lunar month is expected to contain exactly one major term, and the month takes its number from the term it contains, so the eleventh month is by definition the one holding the winter solstice. When a lunar month falls entirely between two major terms and contains none, it is declared intercalary and repeats the number of the month before it, which is how a thirteenth month is inserted without any fixed rule about when.
Qiufen is the autumn equinox, the sun at 180 degrees, and day and night are of equal length. Since 2018 the day has been observed in China as the Farmers' Harvest Festival, a national observance established by the State Council, which is a recent addition rather than a traditional one and is recorded here as such. The equinoxes and solstices are the four terms an observer can determine directly, and the other twenty are interpolated between them.