Tomatoes are fruits that are considered vegetables by nutritionists. Botanically, a fruit is a ripened flower ovary and contains seeds. Tomatoes, plums, zucchinis, and melons are all edible fruits, but things like maple "helicopters" and floating dandelion puffs are fruits too.
Now, nutritionally, the term "fruit" is used to describe sweet and fleshy botanical fruits, and "vegetable" is used to indicate a wide variety of plant parts are not so high in fructose.
There is no hard-and-fast rule that clearly designates a botanical fruit as a vegetable, but, given that tomatoes are generally not used in desserts and are closely related to other gruit-vegetables (e.g., eggplants and peppers), it is not too counterintuitive for tomatoes to be classified as vegetables.
So go ahead and call a tomato whatever you want - it's super tasty either way!
Written by Melissa Petruzzello at Britannica Encyclopedia