Noun. Metaphoric phrase most commonly used to describe a highly unusual or unforeseen event or occurrence. Can be extended to describe
people who are not as they first appear, or when a person acts out of character.
Originally derived from a quotation in '90s cartoon television show "The Tick" in which the eponymous hero, upon seeing a
pig on a rooftop, exclaims "Roof
Pig! Most unexpected!".