night owls; people who stay up late
Refers to people who habitually stay up late at night, often used in a light or self-deprecating way. Not a formal demographic term.
He's a total night owl, always staying up until 3 a.m.
As a night owl, morning meetings are tough for me.
Compound of 深夜 (shin'ya, 'late night') and 族 (zoku, 'tribe' or 'group'), literally 'late-night tribe'. The 族 suffix is commonly used to label social groups or subcultures.