expression, noun
short month; month with fewer than 31 days
Refers to months with 30 or fewer days (February, April, June, September, November). Often contrasted with 大の月 (long month, 31 days).
See also: 大の月
小の月は、月末の日付に注意が必要です。
For short months, you need to be careful with the dates at the end of the month.
2月は小の月で、28日か29
February is a short month, with only 28 or 29 days.