Select the most appropriate meaning of the given idiom.
When pigs fly

The idiom "when pigs fly" is a well-known figurative expression used to describe something that is highly unlikely or completely impossible to occur.

Here is a step-by-step breakdown of why this is the correct meaning:
1. Literal Impossibility: Pigs are flightless animals that lack wings or any physiological capability to fly. Therefore, the literal event of a pig flying will never occur.
2. Figurative Usage: When someone says an event will happen "when pigs fly," they are using hyperbole to link that event to an impossible occurrence. It is a humorous way of saying that the event has a zero probability of happening.
3. Evaluating the Options:
- "Something that will never last long" describes temporary situations, which is incorrect.
- "Something that will never deviate" refers to consistency or predictability, which is incorrect.
- "Something that will get completed" implies success or fulfillment, which is the opposite of the idiom's meaning.
- "Something that will never happen" aligns perfectly with the concept of an impossible event.

Therefore, the most appropriate meaning of the given idiom is "Something that will never happen".