In the lunisolar calendar, a cycle of 7 leap months in 19 years was called 'Sho' (a chapter) and the year, in which an old chapter was replaced by a new one, was named 'Shoshu,' meaning the first year of the new chapter.
太陰太陽暦では、19年7閏の周期を「章」と称し、古い章から新しい章への切替となる年を新しい章の最初の年という意味で「章首」と呼んだ。