Full form of MOM is Middle of Month

Middle of Month is an often-used term to reference the date near the mid of a month. For a 30-day long month like April, middle of the month occurs at midnight of 15th day, however for a 31-day month like January, middle of the month happens at noon of 16th day.

Similarly, for 28-day February month (in a non-leap year), the middle of the month happens at midnight of 14th day, and in case of a leap year February (29 days), the middle of the month occurs at noon of 15th day.