Probably just the name of the secret ending (though that may be the titles before the sections of ending) or the project name, as said, or just a little fun name to give the players an idea of what's to come.
Here is something I would like to know though. I imagine that everyone saying "Sora" are doing so at the same time, to build on the effect of it, as it would be kind of pointless otherwise. Does this mean then, in the case of the RAX trio and Namine, that it's a kind of metaphysical thing? Like that RAX and Nami are still alive somewhere, perhaps in their own kind of world?
I read something about the RAX scene happening during Days, and something changes to make them say it.