The onion (Allium cepa) (Latin 'cepa' = onion), also known as the bulb onion or common onion, is used as a vegetable and is the most widely cultivated species of the genus Allium. This genus also contains several other species variously referred to as onions and cultivated for food, such as the Japanese bunching onion (A. fistulosum), the Egyptian onion (A. ×proliferum), and the Canada onion (A. canadense). The onion is most frequently a biennial or a perennial plant, but is usually treated as an annual and harvested in its first growing season.
Onions are cultivated and used around the world. As a foodstuff they are usually served cooked, as a vegetable or part of a prepared savoury dish, but can also be eaten raw or used to make pickles or chutneys. They are pungent when chopped and contain certain chemical substances which irritate the eyes. Onions contain phenolics and flavonoids that have potential anti-inflammatory, anti-cholesterol, anticancer and antioxidant properties.