The onion belongs to the Liliaceae family, known for its richness in highly volatile and pungent sulphurous essential oils. Its shape can vary between spherical and ellipsoidal, and its diameter varies between 3 and 10 cm, and its weight is between 100 and 250 gr. The color of the onion differs depending on the variety, and ranges from white to purple, passing through yellow and intense red. The onion has a spicy taste, however, there are varieties that even offer a sweet taste.

The origin of the onion is uncertain. While some sources place it in Central Asia, others place it in Western Asia, and there are even those who place it in North Africa. In ancient Egypt, as in ancient Greece and Rome, it was a highly valued product. It was the ancient Romans who introduced its cultivation in the Mediterranean area. The colonizers introduced it to America, being immediately accepted in the area. Its cultivation is common in temperate climates.

Onions have a low caloric value because the key element in their composition is water. The high level of fiber as well as that of minerals (potassium, calcium, iron, magnesium and phosphorus), and vitamins (especially vitamin B, and to a lesser extent vitamins C and E) in its composition must be taken into account. The combination of its low caloric level, together with its high level of fiber that produces a feeling of satiety, makes it an ideal product for people who want to follow a slimming regimen. On the other hand, its high level of potassium gives it diuretic effects. However, its nutritional properties are the most outstanding in its composition, specifically, the large number of antioxidants it has (flavonoids and sulfur compounds). The former, favoring blood action, and the latter beneficial in case of respiratory conditions.

The onion can be consumed both raw -in salads-, as well as cooked, both roasted and boiled, sautéed, fried or sautéed. It is usually used as a garnish in fish, meat, vegetable dishes..., as an ingredient in sauces, purees and creams, or in soup, such as the famous, not without reason, "onion soup".

Before being cut, they can be stored in a cool and dry place, however, once cut, they must be protected with plastic film and kept in the refrigerator.