Small pieces or fragments, especially after something has been smashed or broken into many parts.
When something is in smithereens, it is usually because it has been broken or destroyed into very small pieces.
Examples:
The vase fell and broke into smithereens.
The explosion blew the building into smithereens.
I dropped the plate and it shattered into smithereens.
The kids smashed the pinata into smithereens.
The car crashed into the wall and broke into smithereens.
The old toy was hit by the hammer and it broke into smithereens.