The twenty-four solar terms divide the ecliptic into equal arcs of fifteen degrees, and this one falls at 120 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.
Dashu, major heat, is the last of the summer terms and the hottest point of the year in the climate the system describes. It falls within the sanfu period counted from the summer solstice, so the two ways of naming the height of summer, by solar term and by the fu count, overlap without coinciding. That kind of overlap is common in the Chinese calendar, which carries several independent cycles at once and does not reduce them to each other.