last quarter moon; third quarter moon; waning half-moon
Astronomical term for the moon phase when the left half is illuminated (in the Northern Hemisphere). Often contrasted with 上弦の月 (first quarter moon).
See also: 上弦の月
Tonight the last quarter moon is clearly visible.
The third quarter moon can be seen in the southern sky around dawn.
Compound of 下弦 (last quarter) and 月 (moon). 下弦 literally means 'lower bowstring', referring to the shape of the moon in its waning phase.