Full Moon (FM) Betta
The Full Moon (FM) Betta is a fancy marketing term used to describe a Double Tail Halfmoon Betta.
You will occasionally see this term used on YouTube and on AquaBid auctions.
Since a Single Tail Betta with a 180 degree tail spread is referred to
as a Halfmoon Betta; you can reason that a Double Tail Betta has two
halves (or Half Moons) that make it into a Full Moon Betta.
Whatever you call them, they are still just Double Tail Half Moon Bettas.
Let's hear it for creative marketing....