The difference between fruits and vegetables depends on whether the botanical or culinary definition is used. In botanical terms, a fruit is a seed-filled structure that develops from a flowering plant. Every other part of a plant, including the roots, leaves and stems, is considered a vegetable. In culinary terms, fruits that are savory are referred to as vegetables.
As a result of the discrepancy in the definitions of fruits and vegetables between the botanical and the culinary traditions, there is considerable overlap between the two categories.
From a botanical standpoint, apples, oranges, squash, eggplants, tomatoes, bell peppers and sunflower seeds are all technically fruit. However, from a culinary standpoint, squash, eggplants, tomatoes and bell peppers are considered vegetables because they are used in savory dishes, while sunflower seeds are classified as seeds, a different culinary category altogether.
From both a botanical and a culinary standpoint, beets, turnips, potatoes (roots), lettuce, spinach and kale (leaves), and celery and broccoli (stems) are all considered vegetables.
The confusion between fruits and vegetables is evident as far back as 1893 when the United States Supreme Court had to decide whether to tax tomatoes as fruits or vegetables. The vote for classifying tomatoes as vegetables was unanimous.