To secretly do a second job on the side, often at night, usually without your main boss knowing. You’ll hear it as moonlight as something, meaning you’ve got a sneaky extra gig for a bit of cash. Not always shady, just low key. Honestly, it’s the classic move when rent’s rinsing you.
"Thought Dave was skint, turns out he’s moonlighting as a wedding DJ every Saturday. Rocked up in a shiny suit, smashed Mr Brightside, then scarpered before the boss clocked him."