End Of The Month
You know how 月 can also mean month? If you add 末 on there you have the "month end" aka the end of the month.
This is a jukugo word, which usually means on'yomi readings from the kanji. Since 月 has two on'yomi readings, here's a mnemonic to help you remember which one to use:
When it's the end of the month, everybody gets mats (げつまつ). We don't pay people in money at Tofugu, but everyone gets mats at the month end instead.
By the end of the month, I will leave this apartment.
The party is at the end of the month.
The money from the part-time job comes in at the end of the month.