Bolbbalgan4 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 is "puberty" in English. In Korean, the pronunciation of is the same as , so the group name is sometimes shortened to Bol4.The duo went on a temporary hiatus due to Ahn's music classes requirements in the first half of 2018. Bolbbalgan4 signed with King Records and debuted in Japan on June 5, 2019, with the mini-album Red Planet.On April 2, 2020, Shofar Music announced that Woo Ji-yoon had left the duo, and Ahn Ji-young will continue to promote as Bolbbalgan4.