An expression used to describe a 0% chance of
something ever happening. This means that the event is completely
impossible, no longer exists, and will never
happen.
Example 1:
Person A: "Do you think they'll ever bring back the original Times
Square Toys "R" Us with the indoor Ferris wheel?"
Person B: "Yeah, when pigs
fly. That space is a Gap now."
Example 2:
Person A: "I'm waiting for the MTA to bring back the V train and paper MetroCards."
Person B: "Keep waiting. That'll happen when pigs
fly."