This is really two questions: “What is the difference between a fruit and a vegetable?” and “What is a pickle?”
Let’s deal first with the difference between fruits and vegetables. In botany – the study of plants – a fruit is defined as the part of a plant that contains the seeds. By this definition, apples, oranges, bananas, and melons are fruits. But so are avocados, beans, chili peppers, squash, tomatoes, and cucumbers – all of which we usually call vegetables, not fruits! Other plant products usually classified as vegetables include tubers (like potatoes, carrots, and radishes), bulbs (like onions), and the leafy tops of plants (like lettuce, rhubarb, and spinach). In culinary art – the art of cooking – the main difference between fruits and vegetables is their sweetness.
Pickling is the process of soaking a fresh food item in salt water or vinegar. This keeps the food from spoiling for much longer than would be possible otherwise. We are so used to putting food in the refrigerator that it is easy to forget what a new and amazing thing it is. Refrigeration technology has been around for more than a hundred years, but most of the people in the world still do not own a refrigerator (about a quarter of the world’s population does not even enjoy access to electricity). So most people have always had to find other ways of keeping food edible, and pickling it is a tasty way to make that possible.
When you mention pickles, most people think of pickled cucumbers: by far the most popular pickled product in the USA. But there are many other kinds of pickles enjoyed all over the world, and not all of them are fruits or vegetables. In Mexico, pickled jalapeños are eaten much more frequently than pickled cucumbers. People in India love pickled mangoes, and pickled plums are popular in Japan. British folks eat pickled onions and pickled eggs, and Norwegians eat pickled fish. There are more than likely a few jars of pickled pigs’ feet on the shelf at your local grocery store, although I have never seen anyone buy them!
Whatever kind of pickle you prefer, you are eating an interesting and very useful piece of history. Yum!