beginning of the month
Refers to the first few days or the early part of a month. Often used in business or scheduling contexts. Compare with 月初め (つきはじめ), which is more colloquial.
See also: 月初め
We issue invoices at the beginning of the month.
The beginning of the month is always busy.
月末 refers to the end of the month, while 月初 refers to its beginning.
Compound of 月 (げつ, 'month') and 初 (しょ, 'beginning'). The reading げっしょ results from a regular sound change where げつ + しょ becomes げっしょ.