The twenty-four solar terms divide the ecliptic into equal arcs of fifteen degrees, and this one falls at 135 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 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.
Liqiu opens the autumn at 135 degrees, the midpoint between the summer solstice and the autumn equinox. The name means the establishment of autumn, and it belongs with Lichun, Lixia and Lidong in the group of four season-opening terms. In practice the hottest weather of the year in much of China falls after Liqiu rather than before it, and the discrepancy between the calendar's seasons and the observed climate is old and well recognised in the agricultural literature.