To ride a bit off jorick in the end, why not have it have a few different names, such as Worlds, Universe,ect, as just using one for everything doesn't best describe the RP as a whole.

If it's a fantasy RP They could use Realm to better set the mood. A modern day RP can use world, A futurist RP where they explore other worlds, and stuff better fits universe, but so does Alternate Universe RP of well known fiction. 

So just give them ability to call it any of them when creating it, rather then limiting it to just one name