What's (really) the difference between fruit and vegetables?
There is no real black and white definition of that difference, because where the line is drawn varies from crowd to crowd.


  Botanically speaking, a fruit is a seed-bearing structure that develops from the ovary of a flowering plant, whereas vegetables are all other plant parts, such as roots, leaves and stems. By those standards, seedy outgrowths such as apples, squash and, yes, tomatoes are all fruits, while roots such as beets, potatoes and turnips, leaves such as spinach, kale and lettuce, and stems such as celery and broccoli are all vegetables.
  
  The outlook is quite different in culinary terms, however. A lot of foods that are (botanically speaking) fruits, but which are savory rather than sweet, are typically considered vegetables by chefs. This includes such botanical fruits as eggplants, bell peppers and tomatoes.


You can find the whole article HERE, including this nice graph that I think nicely illustrates things.