In string theory, the word "orbifold" has a slightly new meaning. For mathematicians, an orbifold is a generalization of the notion of manifold that allows the presence of the points whose neighborhood is diffeomorphic to a quotient of R"n" by a finite group, i.e. R"n"/"Γ". In physics, the notion of an orbifold usually describes an object that can be globally written as an orbit space "M"/"G" where "M" is a manifold (or a theory), and "G" is a group of its isometries (or symmetries) — not necessarily all of them. In string theory, these symmetries do not have to have a geometric interpretation.