Literally 'night earning'. Can refer to any legitimate night job, but also used euphemistically for burglary or other illicit nighttime activities. Context determines the meaning.
He is a student during the day and works at a convenience store as a night job.
警察は連続夜稼ぎ事件の犯人を追っている。
The police are pursuing the perpetrator of a series of burglaries.
Compound of 夜 (night) and 稼ぎ (earning, work). The euphemistic sense likely arose from the idea of 'working' at night to steal.