The twenty-four solar terms divide the ecliptic into equal arcs of fifteen degrees, and this one falls at 105 degrees of the sun's apparent longitude. It is a sectional term, a jie, one of the twelve that fall in the odd positions of the twenty-four and open the twelve solar months. The sectional terms and the major terms alternate strictly around the year, so a jie is always followed by a zhong fifteen degrees later.
The terms have not always been spaced the same way. Until the seventeenth century they were reckoned by equal intervals of time, dividing the year into twenty-four equal parts, a method called pingqi. The Shixian calendar, prepared with Jesuit assistance and promulgated in 1645, redefined them by equal intervals of the sun's apparent longitude instead, fifteen degrees apart, which is the definition still used. Because the Earth's orbit is elliptical the sun does not move at a uniform apparent rate, so the intervals between terms now vary by about a day between the shortest and the longest.
Xiaoshu, minor heat, is the first of the pair of heat terms that run through the height of summer, with Dashu following it. The pairing of a lesser and a greater term is one of the organising devices of the list, and it allows a single climatic condition to be given two positions fifteen degrees apart rather than one, which is a more useful division for practical purposes than a single named point would be.