It’s the symbol of the world that refers to the world tree, which is important to the world. During the Medzio Diena “event” the world tree massively overgrew, the goddesses say that the Demons made it do that.
The world tree overgrowing also produced massive amounts of monsters in the world. This is why so much in the game is about plant enemies. All plant enemies were produced by the Medzio Diena disaster 4 years prior to the start of our time in the gameworld.
If I recall correctly it’s supposed to be at the centre of the capital city, which we have not yet visited in game. Apparently completely destroyed in the event.