gugudan (구구단) was a eight-member girl group under Jellyfish Entertainment. Originally as nine, they debuted on June 28, 2016 with the mini album "Act.1 The Little Mermaid". Their name stands for 'multiplication table' in Korean, and represent the nine different charms of each member. In January 2016, members Nayoung, Sejeong, and Mina represented their company in survival reality show, Produce 101, and all three managed to make it to the finals together. In the end, only Sejeong and Mina were the only one to make it to the final lineup of I.O.I, debuting afterwards.
In July 2017, Jellyfish Entertainment formed the subunit group named Gugudan 5959 (Korean: 구구단 오구오구; spelled as "Ogu-ogu"), composed of the youngest members Mina and Hyeyeon.
In June 2018, Jellyfish Entertainment formed the second subunit of Gugudan, composed of members Sejeong, Mina and Nayoung, named Gugudan SeMiNa. The "SeMiNa" name is made up of the first syllables of the members' names. Gugudan SeMiNa debuted with the release of their self-titled single album consisting of two tracks on July 10, 2018
Hyeyeon left the group for personal reasons in October 2018.
Chinese member Sally participated in the Chinese version of survival show Produce 101, Produce Camp 2020, in April. The survival show concluded with Sally ranking sixth, making her a member of the temporary girl group BonBon Girls 303.
On December 30, 2020, Jellyfish Entertainment announced that the group would be ending their activities on December 31.
Korean: 미미
Japanese: ミミ
Korean: 신연서
Korean: 해빈
Japanese: ヘービン
Korean: 소이
Japanese: ソイ
Korean: 나영
Japanese: ナヨン
Korean: 세정
Japanese: セジョン
Korean: 류사저
Japanese: サリー
Korean: 미나
Japanese: ミナ