What is the meaning of idiom back and belly?

The idiom "back and belly" is not a common idiom in English. It's possible you're thinking of a different phrase, or that it's a regional or colloquial expression.

Could you please provide more context? For example:

* Where did you hear this idiom?

* What was the sentence or situation it was used in?

With more information, I can help you understand the intended meaning.