Vegetable is a term which generally refers to an edible part of a plant. The definition is traditional rather than scientific and is somewhat arbitrary and subjective. All parts of herbaceous plants eaten as food by humans, whole or in part, are normally considered vegetables. Mushrooms, though belonging to the biological kingdom Fungi, are also commonly considered vegetables. In general, vegetables are thought of as being savory, and not sweet, although there are many exceptions. Nuts, grains, herbs, spices and culinary fruits are normally not considered vegetables.

Since 'vegetable' is not a botanical term, there is no contradiction in referring to a plant part as a fruit while also being considered a vegetable (see diagram). Given this general rule of thumb, vegetables can also include leaves (lettuce), stems (asparagus), roots (carrots), flowers (broccoli), bulbs (garlic), seeds (peas and beans) and botanical fruits such as cucumbers, squash, pumpkins, and capsicums (bell peppers). Botanically, fruits are reproductive organs (ripened ovaries containing one or many seeds), while vegetables are vegetative organs which sustain the plant.

Vegetables are eaten in a variety of ways as part of main meals and as snacks. The nutrient content of different types varies considerably. With the exception of pulses, vegetables provide little protein and fat.[3][4] Vegetables contain water soluble vitamins like vitamin B and vitamin C, fat-soluble vitamins including vitamin A and vitamin D, and also contain carbohydrates and minerals and fiber. Among the nutrients vegetables may have include antioxidants, antibacterial, antifungal, antiviral, anticarcinogenic nutrients. Also, decaying or rotting vegetables (plant matter in general) may have reduced nutrients, but are often full of probiotic bacteria.

The green color of leafy vegetables is due to the presence of the green pigment chlorophyll. Chlorophyll is affected by pH and changes to olive green in acid conditions, and bright green in alkaline conditions. Some of the acids are released in steam during cooking, particularly if cooked without a cover. The yellow/orange colors of fruits and vegetables are due to the presence of carotenoids, which are also affected by normal cooking processes or changes in pH. The red/blue coloring of some fruits and vegetables (e.g. blackberries and red cabbage) are due to anthocyanins, which are sensitive to changes in pH. When pH is neutral, the pigments are purple, when acidic, red, and when alkaline, blue. These pigments are very water soluble.