Good description (& no mention of tomatoes):
living/nutrition-and-healthy-eating/ expert-blog/fruit-vegetable-difference/ bgp-20056141
According to botanists (those who study plants) a fruit is the part of the plant that develops from a flower. It's also the section of the plant that contains the seeds. The other parts of plants are considered vegetables. These include the stems, leaves and roots — and even the flower bud.
The following are technically fruits: avocado, beans, peapods, corn kernels, cucumbers, grains, nuts, olives peppers, pumpkin, squash, sunflower seeds and tomatoes. Vegetables include celery (stem), lettuce (leaves), cauliflower and broccoli (buds), and beets, carrots and potatoes (roots).