The onion (Allium cepa L.) is a bulbous plant traditionally attributed to the Liliaceae family, according to more recent taxonomic schemes to be included among the Amaryllidaceae, lives underground and is formed by modified leaves, which have an epidermis (protection). It is a biennial herbaceous plant whose life cycle, in cultivation, is interrupted for one year in order to be destined for consumption. It has superficial roots, with leaves that swell in the basal portion, making the edible part. It forms a long floral stem that bears an umbrella inflorescence with yellowish-white flowers. The fruit is a capsule.

Its main use is that of food and seasoning, but it is also used for therapeutic purposes thanks to the properties attributed to it by the science and traditions of folk medicine.

There are many varieties of onions, which generally take their name from the cultivation area, the shape, the color, the size of the bulb, the earliness or, more generally, the color of the external tunics (i.e. the skin that covers the inner globe ). Such peel can be white, golden-yellow or red.