Secret (Korean: 시크릿; Japanese: シークレット, often stylized as SECRET) is a South Korean K-pop girl group formed by TS Entertainment in 2009. Consisting of four members, Jeon Hyosung, Jung Hana, Song Jieun and Han Sunhwa, the group released their debut single, "I Want You Back" on October 13, 2009. In 2010, they released two mini albums entitled Secret Time and Madonna with lead singles "Magic" and "Madonna" respectively. In 2011, Secret released three other singles, namely "Shy Boy", "Starlight Moonlight" and "Love is Move". Jieun, the main vocalist, also released a solo single titled "Going Crazy" featuring B.A.P's leader, Bang Yong Guk. In August 2011, the group made their official debut in Japan. Secret was the third Korean girl group to debut in the top ten on the Oricon charts, with Kara and Girls' Generation being the first and second groups respectively. In October 2011, Secret released their first full-length studio album, Moving in Secret. Aside from their commercial accomplishments, Secret is well known for their transitions to cute and the girl-next-door image through songs like "Shy Boy" and "Starlight Moonlight" from the sexy and powerful image back in 2009 and 2010. In support of their 2nd Japanese single, "So Much For Goodbye", the group embarked a promotional tour in Japan named "Secret 1st Japan Tour" held on March 2012. In September 2012, Secret released their 3rd mini-album entitled Poison after almost a year of absence in the South Korean music industry due to Japanese.
Source : wikipedia