'Youngkeukeu' is a slang term that comes from the group Cortis's track 'Young Creator Crew' (YOUNGCREATORCREW), and it refers to people who are young and on-trend.
Derived variants like 'Neulkeukeu' ('Neulgeun Creator Crew,' meaning 'Old Creator Crew') and 'Neulkeukeu' ('Old Creator Crew') carry the opposite meaning.