noun
Compensation for working beyond regular hours; a standard term in Japanese employment contexts.
今月は残業が多かったので、居残り手当がかなりついた。
I had a lot of overtime this month, so I got a fair amount of overtime pay.
残業手当 is a more common synonym for overtime pay. 居残り手当 is slightly less frequent but carries the same meaning.
Compound of 居残り (staying behind, from 居る 'to be' + 残る 'to remain') and 手当 (allowance, pay).