From a botanical standpoint, the rule is almost too easy. A fruit develops from the flower of a plant and contains seeds. A vegetable is any other edible part, like the leaves, stems, or roots.
This means tomatoes, peppers, and cucumbers are, without a doubt, fruits. They are the plant’s reproductive pods. Meanwhile, spinach, carrots, and celery are vegetables—they are the body of the plant.
It’s a classic case of identity crisis. The plant doesn’t care about our kitchen labels; it just wants to make more plants.