The phrase 'When Pigs Fly' refers to something that is highly unlikely to ever happen.
Example of use: "I might wake up early tomorrow to clean my room". "Yes, you'll do that when pigs fly".
Interesting fact about When Pigs Fly
There have been many mentions of flying pigs throughout history, and there’s some argument about the origin of the idiom “when pigs fly.” The most general consensus is that the term originated either in Germany or Scotland, as there are plenty of examples of its use as a way to describe something that is physically impossible.
