The counterpart to a black hole. In a black hole matter collapses inward to a singularity; in a white hole, matter pours out from a singularity. There are many similarities between the Big Bang and a white hole.
As well as black holes and white holes, relativists sometimes talk about grey holes.
The alteration or outright disappearance of inconvenient or embarrassing documents, photographs, transcripts, or other records, such as from a web site or other archive. Its origin comes from George Orwell's "1984", in which the memory hole was a small incinerator chute used for censoring, (through destroying), things Big Brother deemed necessary to censor.
Person One: "Did you hear about that scandal involving the President?"
Person Two: "Yeah! Looks like someone didn't have time to visit the memory hole."
Dude One: "Yo bro, I like that picture on Facebook of you wearing the "I Love Barry Manilow" shirt!"
Dude Two: "Yeah, that's definitely going in the memory hole."
Strange phenomenon that occurs when one browses through internet smut, then realises that four hours have passed, and they've been spent looking at porn. Often accompanied by huge sense of self-loathing.