Earth-30847 is the designation given to the particular version of the Earth featured in the Marvel vs. Capcom series of video games. In this universe, characters from the Marvel and Capcom franchises are shown to co-exist. It has been said, however, that the two sets of characters are from their own universes, linked via some sort of rift.
This universe is part of what's known as the multiverse, the continuum of Marvel universes, based on the theory of infinite realities. According to Marvel canon, characters from the other universes (such as Earth-616, the main Marvel universe) could conceivably visit this universe. The likelihood of this is slim, however.