Leek is a biennial herbaceous plant of the same family as garlic and onion. Unlike these, however, it does not appear as a rounded bulb or divided into wedges, but rather as a cylinder made of overlapping leaves (called sheaths), white in the part that develops underground and green in the aerial one. The latter is usually eliminated or used in minimal part, while the former is used sliced or in logs.

Leek is used as an aromatic plant in the same way as onion but also as a side dish or in soups.