Korean mun is a type of currency that was used in Korea a long time ago, before they started using the Korean won. Currency is like special pieces of paper or metal that we use to buy things like toys and candy.
Mun were like coins that people used to buy things, except they weren't round like regular coins that we see today. They were shaped like long, skinny rectangles.
Each mun had pictures on them, like a person or an animal. Just like how we can see who is on a dollar bill or a coin, people in Korea could look at the pictures on the mun to tell how much they were worth.
Nowadays, we don't use mun anymore, but we can still see them in museums and sometimes people use them as decorations or collectibles.