Zero is the original survival world on Minr. It was the only world before Theta and Delta were created. When Theta was created, Resource Parkour was closed to make Zero pure survival. WorldEdit and scripts are no longer given in Zero. The zero world is 32k blocks by 32k blocks. Zero has a nether and an end, and since 1.13 Theta and Delta have these too.
Since Zero was the original world, many of the courses are hosted in this world. Additionally, the world was never reset. This made it rather unfit for pure survival, causing the inception of Delta. Now Zero is no longer used for building, nor for pure survival. It has mostly become a legacy world where our old builds are held.
The server ip has Zero in it because Zero was the original world on minr.