げじゅん下旬gejun
1.
A period within a month that spans approximately the last ten days, specifically from the 21st to the last day of that month.
2.
The latter part of a month, emphasizing the final days leading up to the end of the month.
3.
The time frame during which the month transitions from its middle to its conclusion, characterized by the days following the 20th.
Example:
８月下旬に彼らは繁殖のために長い旅に出発します。