Ding is the fourth of the ten Heavenly Stems (tiangan). Its element is Fire and its polarity is yin, so Ding is glossed as yin Fire, likened in tradition to a candle flame or lamplight, smaller and more contained than the blazing yang Fire of Bing but steady and illuminating. As one of the ten stems it pairs with the twelve Earthly Branches to build the sexagenary cycle of sixty used to number years, months, days, and double-hours. Each of the five phases appears among the stems once as yang and once as yin, and Ding carries the yin aspect of Fire. These are the conventions of the Chinese calendrical and cosmological tradition, drawn on in the almanac and in the four-pillars art of fate calculation.
Ding is the fourth Heavenly Stem, paired with Bing under the Fire phase but carrying the Yin polarity, likened traditionally to a candle, lamp or hearth fire rather than Bing's sun, a contained and tended flame instead of a blazing one. As an even-numbered stem it combines only with the six Yin Earthly Branches, Ox, Rabbit, Snake, Goat, Rooster and Pig, within the sixty-term sexagenary cycle used to name years, months, days and hours. In four pillars (BaZi) astrology a Ding day master is read as warm but more focused and inward than a Bing day master, giving steady illumination rather than heat that spreads unchecked, and the tradition associates the stem with refinement, culture and careful attention. Ding also has a long administrative use as an ordinal marker, the fourth item in a list, paralleling the way Jia through Gui once numbered examination results and official rankings before Arabic numerals became standard.