In philosophy, a person who believes that the actual word (the one that we have empirical evidence of) is the only world that exists. This may allow for belief in the existence of the mind or soul, but not other possible worlds, or parallel universes.

Actualism
Ersatzism

Ac"tu*al*ist, n.

One who deals with or considers actually existing facts and conditions, rather than fancies or theories; -- opposed to idealist.

J. Grote.

© Webster 1913.