The phrase "when pigs fly" is an old saying used to describe something impossible.

The saying 'when pigs fly' has been around since the 1600s. People use it to say that something will never happen because pigs are not made to fly. It’s a fun, sarcastic way to talk about things that are very unlikely or impossible. This phrase appears in many cultures, not just English-speaking ones, showing that it’s a common way to joke about impossibility.