carried over from last month; left unpaid from previous month
Used especially for bills, payments, or tasks that remain unsettled and are carried into the current month.
先月の家賃が月越しになっている。
Last month's rent has been left unpaid.
月越しの仕事を早く片付けなければならない。
I have to quickly clear up the work carried over from last month.
Compound of 月 (tsuki, 'month') and 越し (goshi, from 越す kosu, 'to pass over'). Literally 'passing over the month', referring to something that remains from the previous month.