Onion, also known as ball onion, round onion, or jade onion, is a biennial herbaceous plant of the Allium genus in the Liliaceae family. It is native to western and southwestern Asia, as well as Central Asia, and is widely cultivated in countries such as China, India, and the United States. China is one of the world's major production areas.

The part we consume is its thick bulb, which is nearly spherical to flattened spherical in shape. The outer skin has colors such as purple red, yellow, and white, and the inner skin is thick and fleshy. Onions are rich in nutrients, including carbohydrates, proteins, various vitamins, minerals such as calcium, iron, and selenium. They also contain active substances such as sulfur-containing compounds and flavonoids, which have antibacterial, antioxidant, and sugar lowering effects. They are known as the "edible heart stent".

Onion has a unique taste, with a spicy and crisp texture when eaten raw. It is soft and sweet when heated, and can be cold mixed, stir fried, or stewed. It is a versatile ingredient in the kitchen. The volatile substances released when cutting onions can make people shed tears, and refrigerating them before cutting can alleviate this phenomenon. The common varieties are divided into purple skin, yellow skin, and white skin, each with its own specific purpose, and have both edible and medicinal value.