LOONA 1/3 (Hangul: 이달의 소녀 1/3), stylized as LOOΠΔ 1/3, is the first sub-unit of the girl group LOONA. They debuted with members HeeJin, HyunJin, HaSeul and ViVi on March 12, 2017 on Inkigayo with their song "Love & Live".
On April 27, 2017, LOOΠΔ 1/3 had a comeback with a repacked version of their first album, titled Love & Evil.
Although member YeoJin was revealed to be the "/" of 1/3, she is not a member of the unit itself.
The unit's Korean name is pronounced Idalui Sonyeo Sambunui Il (Korean: 이달의 소녀 삼분 일) from the Sino-Korean root meaning "Girl of the Month One Third"; they are also known as LOONA 1/3, often stylized as LOOΠΔ 1/3, which is their official English and Japanese name. In Korean, the "1/3" portion of the name is said as "3/1" (삼분의 일; sambun-ui il, sam being "three" and il being "one"), which is simply the Korean term for one-third.
Since their name consists of Chinese roots, the unit's name is similar in Chinese: in Mandarin Chinese it is pronounced as Běnyuè Shàonǚ Sānfēn zhī Yī (Chinese: 本月少女三分之一).
LOOΠΔ 1/3's music presents itself with a soft concept around the theme of love as the members express the innocence and excitement of having a first crush. In their first album, ‘Love & Live’, the unit sings about the thrill of first love, while in their second album, 'Love & Evil', they sing of the sorrows of heartbreak. The two colliding themes bring together the co-existence of sweetness with the cruelty of first love.
Each member traveled abroad to different countries to represent different locations that are part of the member's individual concepts.
In the LOONAVERSE, HeeJin meets HyunJin, who goes to the same school in the same grade. HaSeul is a warm friend who is like a mother to YeoJin. ViVi, an android who can’t speak Korean very well introduces JinSoul in Hong Kong.
LOOΠΔ 1/3 is a combination of girls present on planet earth. These girls portray the most realistic and practical sceneries that can easily be found on the streets or in school. HeeJin, HyunJin, HaSeul, and ViVi start their stories in France, Japan, Iceland, and Hong Kong to become unified as one.