1.
separate stomach (for dessert)
A playful expression meaning one always has room for dessert or sweets even after eating a full meal, as if desserts go to a 'separate stomach.'
別腹 is an idiomatic expression literally meaning 'separate stomach.'
Usage
Cultural note
This playful expression is commonly used in Japan to justify eating dessert after a full meal. It's similar to the English expression 'there's always room for dessert.'