A night owl is someone who likes to stay awake until late at night, or who works at night.
Examples of use:
1. He's always been a night owl: when he was a child he often read until past midnight.
2. There were a few night owls sitting in the café, but most people had gone home.
3. I'm a night owl: I do my best work at night.
Are you a night owl, or do you prefer to be up with the lark?
Image © Angela GS