taiyuan
A set of heavenly stems and earthly branches derived from the month pillar, representing the month of conception.
A set of stems and branches derived from the month pillar: the month's heavenly stem advances one position, and the month's earthly branch advances three positions. Traditionally, it represents the month of conception.
⚠️ Usage varies greatly among different schools; some emphasize it, while others ignore it entirely. This site only lists the stems/branches and their nayin, without making judgments.