Bolbbalgan4 (Korean: 볼빨간 사춘기, also known as BOL4 or Blushing Youth or Blushing Puberty, pronounced Bolbbalgan Sachungi) is a South Korean musical act formed by Shofar Music in 2016. They appeared on Superstar K6 in 2014 before signing a contract with their current agency. BOL4 was originally a duo consisting of Ahn Ji-young and Woo Ji-yoon. They debuted with the single "Fight Day" from the mini-album Red Ickle on April 22, 2016. The meaning of 사춘기(思春期) is "puberty" in English. In Korean, the pronunciation of 사(思) is the same as 사(四=4), so the group name is sometimes shortened to Bol4.