Quoted from wiki:
"In astrophysics, a white hole is the theoretical time reversal of a black hole. While a black hole acts as a vacuum, drawing in any matter that crosses the event horizon, a white hole acts as a source that ejects matter from its event horizon."
It has also been theorized that white holes are instrumental in the formation of new universes. In fiction white holes are typically viewed as the opposite of black holes with energy output comparable to exploding singularities. (It should be noted that according to most current models of physics, white holes are thermodynamically impossible)
See also: