A preparation technique of splitting an item down the center, nearly completely through, so the halves can be opened and laid flat, looking like a butterfly (though a meaty, dead one.)

I think I already knew that. I guess I just never think of the term while I'm slicing something down the middle. Thanks for posting the definition.

This is a new word for me. I have heard this word from a chef in a cooking program. But I never knew that it that it simply meant splitting. A new addition to my cooking word bank.