White holes are very much related to black holes, although they are completely theoretical. They stem from the belief that black holes end somewhere. There are two places they are believed to end up, if they end. They either end in another place in that Universe, or in another Universe. Therefore, the other side of a black hole is a white hole. This gets its name because theoretically everything is shot out of these, including a massive amount of light. There is a current theory that in the creation of our Universe there were many primordial black holes and white holes created. They were very small and have dissappeared from existance now. That's about it for white holes.