Actually, the first question should be "What is a LOONA?" or "Who is LOONA?"
LOONA is a girl group, consisting of twelve members: Heejin, Hyunjin, Haseul, Yeojin, ViVi, Kim Lip, Choerry, JinSoul, Yves (pronounced as Eve), Chuu, Go Won & Olivia Hye. They've had a really interesting way of debuting: the girls all first debuted solo , then in a unit and then in the full group. (Example: Heejin, Hyunjin, Haseul & ViVi first debuted solo then in the Unit 1/3 and then all 12 girls debuted together in the group. Every member has their own, represantative colours and an animal. The members of the 1/3 Unit have locations, the members of Odd Eye Circle have super powers and the yyxy-members have fruits. These are the units and their members: Yyxy - Yves, Chuu, Go Won & Olivia Hye, Odd Eye Circle - Kim Lip, JinSoul & Choerry, 1/3 - Heejin, Hyunjin, Haseul & ViVi. The only member to not be in a unit is Yeojin, but she kind of represents the "/" in "1/3".
So what is the LOONAverse? The LOONAverse is a fictional universe, where the girls live. There are three worlds: Earth, where 1/3 and Yeojin live, Cosmos, wher Odd Eye Circle live and Eden, where yyxy live. This whole world bases on the Möbius Strip World Theory. These girls have to find each other to "soar up high". There are a ton of theories about the LOONAverse, and everyone can make up one for themselves. My favourite ones are made by Daebak Jjang.