moon of the 13th day of the 9th lunar month
Archaic term for the moon on the 13th night of the 9th month in the old lunar calendar, associated with the harvest moon viewing tradition. See also 十三夜.
See also: 十三夜
後の月 is an old word referring to the moon on the 13th night of the 9th month in the lunar calendar.
leap month
Rare historical term for an intercalary month in the lunisolar calendar. Modern Japanese uses 閏月.
See also: 閏月
後の月 once also meant a leap month.