In its broadest sense, the term vegetable refers to any type of plant life or plant product; in its narrower connotation, it refers to the fresh, edible component of a herbaceous plant consumed raw or cooked.
A root, like rutabaga, beet, carrot, and sweet potato; a tuber or storage stem, like potato and taro; a stem, like asparagus and kohlrabi; a bud, like brussels sprouts; a bulb, like onion and garlic; a petiole or leafstalk, like celery and rhubarb; a leaf, like cabbage, lettuce, parsley, spinach, and chive; a seed, such as pea and lima bean; an immature fruit, such as eggplant, cucumber, and sweet corn (maize); or a full fruit, such as tomato and pepper. It's tough to maintain the popular difference between vegetable and fruit.