A white hole is a hypothetical region of spacetime and singularity that cannot be entered from the outside, but light and matter can escape. It is essentially the opposite of a black hole. In addition to a black hole region in the future, such a solution of the Einstein field equations has a white hole region in its past. This is not true for black holes created through gravitational collapse, however, there aren't any processes observed that create a white hole. They are like black holes in the fact that they both have mass, charge, and angular momentum, and they both attract mass, but nothing can reach the event horizon of a white hole.