Astronomical term for the moon at first or last quarter, when it appears as a half circle. Often used in compounds like 上弦の月 (first quarter moon) and 下弦の月 (last quarter moon).
Specifically the last quarter moon, a subset of 弦月.
Etymology
Compound of 弦 (string, bowstring, crescent) and 月 (moon), referring to the moon's shape resembling a bow. The exact historical derivation is uncertain.
