/muːnlaɪtɪŋ/ – Noun
Definition: Là việc làm thêm ngoài giờ làm việc chính thức.
A more thorough explanation: (informal) the activity of having a second job as well as your regular job, especially a job that you do secretly and in the evenings, at night, or weekends, and do not declare to the tax authorities
Example: The number of Brits moonlighting to supplement their incomes has doubled in just twelve months.