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."