What country uses wen?

Excuse me, but I'm curious about a term I've come across recently: "wen." Could you clarify for me which country specifically utilizes this term, and if it's tied to any particular aspect of their culture, economy, or financial system? Is it a colloquial expression, or does it hold a more formal significance within a specific nation's context? I'm genuinely intrigued and would appreciate any insights you could provide.