Wikipedia
Sogeum
The sogeum (also spelled sogum or sogŭm) is a small bamboo transverse flute used in traditional Korean music. Unlike the larger daegeum, it does not have a buzzing membrane (although it did have one in ancient times). It is used in court, aristocratic, and folk music, as well as in contemporary classical music, popular music, and film scores.
Other larger flutes in the same family include the medium-sized junggeum and the large daegeum; the three together are known as samjuk (hangul: 삼죽; hanja: 三竹; literally "three bamboo"), as the three primary flutes of the Silla period.